Short interfering RNA (siRNA) analogues

ABSTRACT

The present invention is directed to novel double-stranded short interfering (siRNA) analogs comprising locked nucleic acid (LNA) monomers. Such compounds induces sequence-specific post-transcriptional gene silencing in many organisms by a process known as RNA interference (RNAi). The compounds disclosed herein has improved properties compared to non-modified siRNAs and may, accordingly, be useful as therapeutic agents, e.g., in the treatment of various cancer forms. More particularly, the present invention is directed to siRNA analogs comprising a sense strand and an antisense strand, wherein each strand comprises 12-35 nucleotides and wherein the siRNA analogs comprise at least one locked nucleic acid (LNA) monomer.

FIELD OF THE INVENTION

The present invention is directed to novel double-stranded shortinterfering (siRNA) analogues comprising locked nucleic acid (LNA)monomers. Such compounds induces sequence-specific post-transcriptionalgene silencing in many organisms by a process known as RNA interference(RNAi). The compounds disclosed herein has improved properties comparedto non-modified siRNAs and may, accordingly, prove useful as therapeuticagents, e.g., in the treatment of various cancer forms.

BACKGROUND OF THE INVENTION

Discovery of RNA interference (RNAi) in C. Elegans was made by Fire etal. (Nature, 1998, 391, 806-811). Long stretches of double stranded RNA(dsRNA) was found to have a potent knock-down effect on gene expressionthat could last for generations in the worm. RNA interference (RNAi)rapidly became a functional genomic tool in C. Elegans (early RNAinterference is reviewed by Fire (TIG, 1999, 15, 358-363) and Bosher andLabouesse (Nature Cell Biology, 2000, 2, E31-E36)). The first studieswhere RNA interference was demonstrated to work in vertebrates wereperformed in zebrafish embryos and mouse oocytes (Wargelius et al.,Biochem. Biophys. Res. Com. 1999, 263, 156-161, Wianny andZernicka-Goetz, Nature Cell Biology, 2000, 2, 70-75). Since dsRNAinduces non-specific effects in mammalian cells it has been argued thatthese mechanisms were not fully developed in the mouse embryonic system(Alexopoulou et al., Nature, 2001, 413, 732-738, Reviews: Stark et al.,Annu. Rev. Biochem., 1998, 67, 227-264 and Samuel, Clin. Micro. Rev.,2001, 14, 778-809).

As far as C. Elegans and Drosophila are concerned, it has been shownthat the long RNAi strands are degraded to short double strands (21-23nucleotides) and that these degraded forms mediated the interference(Zamore et al., Cell, 2000, 101, 25-33 and Elbashir et al., Gen. Dev.,2001, 15, 188-200). Elbashir et al. (Gen. Dev., 2001, 15, 188-200)showed that a sense or antisense target is cleaved equally and that bothstrands in siRNA can guide cleavage to target antisense or sense RNA,respectively. It was unambiguously shown by Elbashir et al. (Nature,2001, 411, 494-498) that the siRNAs mediate potent knock-down in avariety of mammalian cell lines and probably escaped the adversenon-specific effects of long dsRNA in mammalian cells. This discoverywas a hallmark in modern biology and the application of siRNAs astherapeutics soon became an attractive field of research (Reviewed byMcManus and Sharp, Nature Reviews Genetics, 2002, 3, 737-747 andThompson, D D T, 2002, 7, 912-917).

DsRNAs are rather stable in biological media. However, the moment theduplex is dissociated into the individual strands these are, by virtueof being RNA, immediately degraded. One of the strategies to bringfurther stability to siRNA has been to introduce chemically modified RNAresidues into the individual strands of the siRNA. It is well known thatsynthetic RNA analogues are much more stable in biological media, andthat the increased stability is also induced to the proximate native RNAresidues. By greater stability is mainly meant increased nucleaseresistance but also better cellular uptake and tissue distribution maybe conferred by such modifications. Several siRNA analogues have beendescribed:

Pre-siRNA (Parrish et al. Mol. Cell, 2000, 6, 1077-1087) show tolerancefor certain backbone modifications for RNAi in C. elegans. By in vitrotranscription of the two different strands in presence of modifiednucleotides, it was possible to show that phosphorothioates aretolerated in both the sense and antisense strand and so are2′-fluorouracil instead of uracil. 2′-Aminouracil and 2′-aminocytidinereduce the RNAi activity when incorporated into the sense strand and theactivity is completely abolished when incorporated in the antisensestrand. With an exchange of uracil to 2′-deoxythymidine in the sensestrand the effect is also reduced, and even more when the exchange is inthe antisense strand. If one or both strand(s) consist entirely of DNAmonomers, the RNAi activity is abolished. In the above-mentioned study,base modifications were also investigated; It was found that4-thiouracil and 5-bromouracil are tolerated in both stands, whereas5-iodouracil and 5-(3-aminoallyl)uracil reduce the effect in the sensestrand and even more in the antisense strand. Replacing guanosine withinosine markedly reduces the activity, independently of whether themodification is performed in the sense or antisense strand.

However, UU 3′ overhangs can be exchanged with 2′ deoxythymidine 3′overhangs and are well tolerated (Elbashir et al., Nature, 2001, 411,494-498 and Boutla et al., Curr. Biol., 2001, 11, 1776-1780).

It has also been shown that DNA monomers can be incorporated in thesense strand without compromising the activity.

Elbashir et al., EMBO, 2001, 20, 6877-6888) showed that modified siRNAcontaining four deoxynucleotides in each 3′-end of the siRNA maintainedfull activity. Furthermore, it was found that the activity was abolishedif the siRNA contained only one base-pair mismatch in the “middle” ofthe molecule.

However, it has also been reported that 1-2 mismatches can be toleratedas long as the mismatches are introduced in the sense strand (Nolen etal., NAR, 2002, 30, 1757-1766; Hohjoh, FEBS Lett., 2002, 26179, 1-5;Hamada et al., Antisense and Nucl. Acid Drug Dev., 2002, 12, 301-309;and Boutla et al., Curr. Biol., 2001, 11, 1776-1780)).

Nykänen et al. (Cell, 2001, 107, 309-321) showed the need for ATP inmaking siRNA out of RNAi, but also in the later steps to exert the siRNAactivity. ATP is needed for unwinding and maintaining a 5′-phosphate forRISC recognition. The 5′-phosphate is necessary for siRNA activity.Martinez et al. (Cell, 2002, 110, 563-574) showed that a single strandcan reconstitute the RNA-induced silencing complex (RISC, Hammond etal., Nature, 2000, 404, 293-296) and that a single antisense strand hasactivity especially when 5′-phosphorylated. 5′-antisense strandmodification inhibits activity while both the 3′ end and the 5′ end ofthe sense strand can be modified.

Amarzguioui et al. (NAR, 2003, 31, 589-595) confirmed theabove-mentioned findings, and it was concluded that a mismatch istolerated as long as it is not too close to the 5′ end of the antisensestrand. A mismatch 3-5 nucleotides from the 5′ end of the antisensestrand markedly diminishes the activity. However, it was shown that twomismatches are tolerated if they are in the “middle” or towards the 3′end of the antisense strand, though with a slightly reduced activity.

Modifications, such as phosphorothioates and 2′-O-methyl RNA, have beenintroduced at the termini of siRNA (Amarzguioui et al., NAR, 2003, 31,589-595) and they were well tolerated. 2′-O-allylation reduces theeffect when present in the 5′ end of the antisense strand

The bi-cyclic nucleoside analogue ENA (2′-O,4′-C-ethylene thymidine (ENAthymidine, eT) has also been incorporated into siRNA (Hamada et al.,Antisense and Nucl. Acid Drug Dev., 2002, 12, 301-309). It was shownthat two ENA thymidines in the 5′ end of the sense strand deterioratedthe effect. It was concluded by Hamada et al. (2002) that: “using2′-O,4′-C-ethylene thymidine, which is a component of ethylene-bridgednucleic acids (ENA), completely abolished RNAi”.

More recently, a number of siRNAs containing incorporated LNA monomerswere described by Braasch et al. (Biochemistry 2003, 42, 7967-7975).

In conclusion, it has been shown that the antisense strand is moresensitive to modifications than is the sense strand. Without beinglimited to any specific theory, this phenomena is, at least partly,believed to be based on the fact that the structure of theantisense/target duplex has to be native A-form RNA. The sense strand ofsiRNA can be regarded as a “vehicle” for the delivery of the antisensestrand to the target and the sense strand is not participating in theenzyme-catalysed degradation of RNA. Thus, in contrast to the antisensestrand, modifications in the sense strand is tolerated within a certainwindow even though the modifications induce changes to the A-formstructure of the siRNA. If changes are introduced in the antisensestrand they have to be structurally balanced within the recognitionframe of the native RNA induced silencing complex (RISC).

Evidently, there is a need in the field for novel and improved siRNAanalogues which possess potent in vivo properties, an increasedbiostability (corresponding to an increased T_(m)), an increasednuclease resistance, improved cellular uptake and/or improved tissuedistribution as compared to the siRNA compounds which are presentlyavailable.

Thus, the object of the present invention is to provide improved siRNAanalogues having one or more of the above-mentioned improved properties.The present invention thus provides improved siRNA analogues which,inter alia, show a high degree of biostability and/or nuclease stabilityand which efficiently targets RNA, such as mRNA or pre-mRNA, or avariety of structural RNAs such as tRNA, snRNA, scRNA, rRNA or evenregulatory RNAs like microRNAs

BRIEF DESCRIPTION OF THE INVENTION

Accordingly, in a first aspect the present invention relates to adouble-stranded compound comprising a sense strand and an antisensestrand, wherein each strand comprises 12-35 nucleotides and wherein saidcompound comprises at least one locked nucleic acid (LNA) monomer.

In another aspect the present invention relates to a pharmaceuticalcomposition comprising a compound according to the invention and apharmaceutically acceptable diluent, carrier or adjuvant.

In a further aspect the present invention relates to a compoundaccording to the invention for use as a medicament.

In a still further aspect the present invention relates to the use of acompound according to the invention for the manufacture of a medicamentfor the treatment of cancer or Severe Acute Respiratory Syndrome (SARS).

In an even further aspect the present invention relates to a method fortreating cancer or Severe Acute Respiratory Syndrome (SARS), said methodcomprising administering a compound according to the invention or apharmaceutical composition according to the invention to a patient inneed thereof.

Other aspects of the present invention will be apparent from the belowdescription and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the two furanose conformations (S-type and N-type).

FIG. 2 shows the improved stability of siLNA over siRNA in biologicalfluids. GL3+/− is rapidly degraded while slightly modified siLNA (No.2185/2186) and more heavily modified siLNA (No. 2703-01/2186) exhibit amarkedly improved stability. The stability study was performed in 10%foetal bovine serum in physiological salt solution at 37° C.

FIG. 3 shows the down-regulation of the endogenous NPY gene in PC12cells by siLNAs. The tested compounds were (from left to right): 2ndbar: unrelated siRNA; 3rd bar: NPY+/1, 4th bar: 2796/NPY−; 5th bar:2795/NPY+; 6th bar: NPY+/2797; 7th bar: 2796/2797.

FIG. 4 shows the effect of siLNA in targeting firefly luciferase andmodulation of the expression. The left lines represent the sense strandand the right lines represent the antisense strand of the siLNA. Themarks on the individual lines represent the position of the LNAmonomers. The last two lines on the right represent control siRNA. Thefirst bar (on the left) represents full, non-modulated, luciferasereporter expression to which all samples are normalised. The testedcompounds were (from left to right): 2nd bar: GL3+/−; 3rd bar:GL3+/2186; 4th bar: GL3+/2187; 5th bar: 2184/GL3−; 6th bar: 2184/2186;7th bar: 2184/2187; 8th bar: 2185/GL3−; 9th bar: 2185/2186; 10th bar:2185/2187; 11th bar: 2703-1/GL3−; 12th bar: 2703-1/2186; 13th bar:GL3+/2189; 14th bar: unrelated siRNA.

FIG. 5 shows the effect of siLNA in targeting Renilla luciferase andmodulation of the expression. The left lines represent the sense strandand the right lines represent the antisense strand of the siLNA. Themarks on the individual lines represent the position of the LNAmonomers. The first bar represents full, non-modulated luciferasereporter expression, to which all samples are normalised. The testedcompounds were (from left to right): 2nd bar: RL+/−; 3rd bar:RL+/2699-1; 4th bar: 2700-1/2699-1; 5th bar: 2702-1/2699-1; 6th bar:RL+/2701-1; 7th bar: 2700-1/2701-1; 8th bar: 2702-1/2701-1.

FIG. 6 shows the stability in rat serum of single-stranded oligoscontaining LNA and RNA monomers, double-stranded (ds) RNA andsingle-stranded (ss) RNA. dsRNA and ssRNA were degraded immediatelywhile intact single-stranded oligos containing LNA and RNA monomerscould be detected after 20-40 minutes. The tested oligos were 2189 andthe corresponding ssRNA (GL3−) and dsRNA (GL3+/1).

FIG. 7 shows siLNA and siRNA compounds for targeting SARS. Capitalletters: Beta-D-oxy LNA monomer. Small letters: RNA monomer.

FIG. 8 shows the cytopathic effect (CPE) in vero cells when infectedwith SARS and the reduced CPE after siRNA treatment. Shown is siRNASARS 1. Mock is treated with the transfectionagent lipofectamine 2000alone. Also shown is non-infected cells.

FIG. 9 shows inhibition of SARS-induced cytotoxicity by siRNA and siLNA.The tested compounds were: SARS 1: 2842-1/2843-1; SARS 2: 2872-1/2845-1;SARS 3: 2846-1/2847-1; SARS 4: 2848-1/2849-1 as well as thecorresponding unmodified siRNAs. No difference in the treatment withsiLNA and siRNA could be detected for the most efficient site, SARS 1.The medium efficient site, SARS 3, was improved by siLNA to be asefficient as the SARS 1 site. The two sites that did not shown siRNAefficiency at all, SARS 2 and SARS 4, did not show any effect by siLNAtreatment either. The inhibitory effect is reduced at high viral doses(60,000 TCID50). Controls were luciferase (Luc) and neuropeptide Y (NPY)siRNA and siLNA. No adverse effects were seen by the siLNA controls.Cytotoxicity was measured as lactate dehydrogenase (LDH) release at 50hours post infection. The different graphs represent different viraldoses (tissue culture infectious dose 50, TCID50).

FIG. 10 shows the proposed mechanism of RISC loading where the helicaseis unwinding the siRNA duplex at the weakest binding end.

FIG. 11 shows the effect of single base-pair mismatches incorporatedopposite to the 5′ end of the antisense strand. Lines are RNA, circlesindicate LNA monomers and crosses illustrate mismatch incorporations.The tested compounds were (from left to right): Renilla luciferase: 2ndbar: RL+/−; 3rd bar: RL+/2701-1; 4th bar: RL+(pos. 19A→C)/2701-1; 5thbar: RL+(pos. 19A→C)/−; Firefly luciferase: 2nd bar: GL3+/−; 3rd bar:GL3+/2187; 4th bar: GL3+(pos. 19A→C)/2187; 5th bar: GL3+(pos. 19A-C)/−.

FIG. 12 shows the effect of LNA monomer position in the antisensestrand. Lines are RNA, circles indicate LNA monomers. The testedcompounds were (from left to right): 2nd bar: GL3+/−; 3rd bar:GL3+/2187; 4th bar: GL3+/2789; 5th bar: GL3+/2790; 6th bar: GL3+/2792:7th bar: GL3+/2793; 8th bar: GL3+/2794; 9th bar: GL3+/2864; 10th bar:GL3+/2865; 11th bar: GL3+/2866; 12th bar: GL3+/2867.

FIG. 13 shows the siLNA improvement of medium-efficient target sites.MOCK represents no oligo. Ren1 is the optimal target site for siRNA andRen2 and Ren3 are less potent sites. Lines are RNA and circles indicateLNA monomers. The tested compounds were: Ren1: RL+/−; Ren2:2863/corresponding unmodified antisense strand; Ren3: 2826/correspondingunmodified antisense strand, as well as the corresponding unmodifiedsiRNAs.

FIG. 14 shows the concentration-depending gene silencing effect of siLNAand siRNA.

FIG. 15 shows improved designs of modified siRNAs by incorporation ofDNA and LNA monomers.

FIG. 16 shows the decreased siLNA efficacy by using a LNA monomer with abulky nucleobase (T instead of U) at cleaving position 10 in theantisense strand. The tested compounds were: siRNA: GL3+/−; siLNA10T:GL3+/2865; siLNA10U: GL3+/2865-U.

FIG. 17 shows the inhibition of SARS sense/antisense target in 3′-UTR offirefly luciferase

FIG. 18 shows the in vivo anti-tumour effect of two anti-EGFP siLNAs(3029/3031 and 3030/3031) on 15PC3-EGFP xenograft NMRI mice.

FIG. 19 shows the tumour volume of siLNA-and-saline treated 15PC3-EGFPxenograft NMRI mice using Alzet 1007D minipumps. The tumours wereimplemented at day 0. The treatment was initiated on day 7 andterminated on day 12. As can be seen, the siLNA-treated mice had atumour size corresponding to the control mice.

FIG. 20 shows that siLNA duplexes 3029/3031 are intact after 7 day inAlzet 1007D minipumps.

FIG. 21 shows that siLNA duplexes 3030/3031 are intact after 7 day inAlzet 1007D minipumps.

DETAILED DESCRIPTION OF THE INVENTION Definitions

In the present context the term “nucleotide” means a 2-deoxyribose (DNA)unit or a ribose (RNA) unit which is bonded through its number onecarbon to a nitrogenous base, such as adenine (A), cytosine (C), thymine(T), guanine (G) or uracil (U), and which is bonded through its numberfive carbon atom to an internucleoside linkage group (as defined below)or to a terminal groups (as defined below). Accordingly, when usedherein the term “nucleotide” encompasses RNA units (or monomers)comprising a ribose unit which is bonded through its number one carbonto a nitrogenous base, such as A, C, T, G or U, and which is bondedthrough its number five carbon atom to a phosphate group or to aterminal group. Analogously, the term “nucleotide” also encompasses DNAunits (or monomers) comprising a 2-deoxyribose unit which is bondedthrough its number one carbon to a nitrogenous base, such as A, C, T, Gor U, and which is bonded through its number five carbon atom to aphosphate group or to a terminal group. The term “nucleotide” alsocovers variants or analogues of such RNA and DNA monomers. A detaileddisclosure of such RNA and DNA monomer variants or analogues are givenbelow.

In the present context the term “nucleoside” means a 2-deoxyribose (DNA)unit or a ribose (RNA) unit which is bonded through its number onecarbon to a nitrogenous base, such as adenine (A), cytosine (C), thymine(T), guanine (G) or uracil (U). Accordingly, when used herein the term“nucleoside” encompasses RNA units (or monomers) comprising a riboseunit which is bonded through its number one carbon to a nitrogenousbase, such as A, C, T, G or U. Analogously, the term “nucleoside” alsoencompasses DNA units (or monomers) comprising a 2-deoxyribose unitwhich is bonded through its number one carbon to a nitrogenous base,such as A, C, T, G or U. The term “nucleoside” also covers variants oranalogues of such RNA and DNA monomers. It will be understood that theindividual nucleosides are linked together by an internucleoside linkagegroup.

When used in the present context, the terms “locked nucleic acidmonomer”, “locked nucleic acid residue”, “LNA monomer” or “LNA residue”refer to a bicyclic nucleotide analogue. LNA monomers are described ininter alia WO 99/14226, WO 00/56746, WO 00/56748, WO 01/25248, WO02/28875, WO 03/006475 and WO 03/095467. The LNA monomer may also bedefined with respect to its chemical formula. Thus, a “LNA monomer” asused herein has the chemical structure shown in Scheme 2 below:

wherein

-   -   X is selected from the group consisting of O, S and NR^(H),        where R^(H) is H or alkyl, such as C₁₋₄-alkyl;    -   Y is (—CH₂)_(r), where r is an integer of 1-4; with the proviso        that when X═O then r is not 2.    -   Z and Z* are independently absent or selected from the group        consisting of an internucleoside linkage group, a terminal group        and a protection group; and    -   B is a nucleobase. A detailed disclosure of preferred LNA        monomers are given below.

The term “internucleoside linkage group” is intended to mean a groupcapable of covalently coupling together two nucleosides, two LNAmonomers, a nucleoside and a LNA monomer, etc. Specific and preferredexamples include phosphate groups and phosphorothioate groups.

The term “nucleic acid” is defined as a molecule formed by covalentlinkage of two or more nucleotides. The terms “nucleic acid” and“polynucleotide” are used interchangeable herein. When used herein, a“nucleic acid” or a “polynucleotide” typically contains more than 35nucleotides.

The term “oligonucleotide” refers, in the context of the presentinvention, to an oligomer (also called oligo) of RNA, DNA and/or LNAmonomers as well as variants and analogues thereof. When used herein, an“oligonucleotide” typically contains 2-35 nucleotides, in particular12-35 nucleotides.

By the term “improved properties” is understood one or more property bywhich the siLNA compound of the invention show better overallperformance as compared to its native counterparts. Examples of suchparameters are ease of production, cost of production, longer shelflife, higher binding affinity to target (interim complement in siLNA ormRNA target), higher ability to penetrate a cell membrane, betterresistance to extra- and intracellular nucleases, easier to formulatepharmaceutically, higher potency in mode of action, better tissuedistribution, better phenotypic response, longer lasting effects, etc.

By the terms “unit” or “residue” is understood a monomer.

The term at least one encompasses an integer larger than or equal to 1,such as 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17 and soforth.

The terms “a” and an as used about a nucleotide, a nucleoside, an activeagent, a LNA monomer, etc. is intended to mean one or more. Inparticular, the expression “a component (such as a nucleotide, anucleoside, an active agent, a LNA monomer or the like) selected fromthe group consisting of . . . ” is intended to mean that one or more ofthe cited components may be selected. Thus, expressions like “acomponent selected from the group consisting of A, B and C” is intendedto include all combinations of A, B and C, i.e. A, B, C, A+B, A+C, B+Cand A+B+C.

The term “thio-LNA” refers to a locked nucleotide in which X in Scheme 2is S. Thio-LNA can be in both the beta-D form and in the alpha-L form.Generally, the beta-D form of thio-LNA is preferred. The beta-D form ofthio-LNA is shown in Scheme 3 as compound 3C.

The term “amino-LNA” refers to a locked nucleotide in which X in Scheme2 is NH or NR^(H), where R^(H) is hydrogen or C₁₋₄-alkyl. Amino-LNA canbe in both the beta-D form and alpha-L form. Generally, the beta-D formof amino-LNA is preferred. The beta-D form of amino-LNA is shown inScheme 3 as compound 3D.

The term “oxy-LNA” refers to a locked nucleotide in which X in Scheme 2is O. oxy-LNA can be in both the beta-D form and alpha-L form. Thebeta-D form of oxy-LNA is preferred. The beta-D form and the alpha-Lform are shown in Scheme 3 as compounds 3A and 3B, respectively.

The term “siLNA” is broadly used about the double-stranded compounds ofthe invention. Thus, a “siLNA”, as used herein, always comprises atleast one LNA monomer.

As used herein, the term “siRNA” refers to a double stranded stretch ofRNA or modified RNA monomers. In a typical siRNA compound, the twostrands usually have 19 nucleotides complementary to each other therebycreating a double strand that is 19 nucleotides long and each strandhaving a 3′-end of two overhanging nucleotides. This is not a strictdefinition of siRNA, which may be slightly longer or shorter, and withor without overhangs. In siRNA one strand is guiding and complementaryto the target RNA (antisense strand), and the other strand (sensestrand) has the same sequence as the target RNA and hence iscomplementary to the guiding/antisense strand. Herein, regulatory RNAssuch as “micro RNA” (“miRNA”) and “short RNA” (“shRNA”) and a variety ofstructural RNAs such as tRNA, snRNA, scRNA, rRNA are usedinterchangeably with the term “siRNA”.

As used herein, the term “mRNA” means the presently known mRNAtranscript(s) of a targeted gene, and any further transcripts, which maybe identified.

As used herein, the term “target nucleic acid” encompass any RNA thatwould be subject to modulation, targeted cleavage, steric blockage(decrease the abundance of the target RNA and/or inhibit translation)guided by the antisense strand. The target RNA could, for example, begenomic RNA, genomic viral RNA, mRNA or a pre-mRNA

As used herein, the term “target-specific nucleic acid modification”means any modification to a target nucleic acid.

As used herein, the term “gene” means the gene including exons, introns,non-coding 5′ and 3′ regions and regulatory elements and all currentlyknown variants thereof and any further variants, which may beelucidated.

As used herein, the term “modulation” means either an increase(stimulation) or a decrease (inhibition) in the expression of a gene. Inthe present invention, inhibition is the preferred form of modulation ofgene expression and mRNA is a preferred target.

As used herein, the term “targeting” an siLNA or siRNA compound to aparticular target nucleic acid means providing the siRNA or siLNAoligonucleotide to the cell, animal or human in such a way that thesiLNA or siRNA compounds are able to bind to and modulate the functionof the target.

As used herein, “hybridisation” means hydrogen bonding, which may beWatson-Crick, Hoogsteen, reversed Hoogsteen hydrogen bonding, etc.,between complementary nucleoside or nucleotide bases. The fournucleobases commonly found in DNA are G, A, T and C of which G pairswith C, and A pairs with T. In RNA T is replaced with uracil (U), whichthen pairs with A. The chemical groups in the nucleobases thatparticipate in standard duplex formation constitute the Watson-Crickface. Hoogsteen showed a couple of years later that the purinenucleobases (G and A) in addition to their Watson-Crick face have aHoogsteen face that can be recognised from the outside of a duplex, andused to bind pyrimidine oligonucleotides via hydrogen bonding, therebyforming a triple helix structure.

In the context of the present invention “complementary” refers to thecapacity for precise pairing between two nucleotides sequences with oneanother. For example, if a nucleotide at a certain position of anoligonucleotide is capable of hydrogen bonding with a nucleotide at thecorresponding position of a DNA or RNA molecule, then theoligonucleotide and the DNA or RNA are considered to be complementary toeach other at that position. The DNA or RNA strand are consideredcomplementary to each other when a sufficient number of nucleotides inthe oligonucleotide can form hydrogen bonds with correspondingnucleotides in the target DNA or RNA to enable the formation of a stablecomplex. To be stable in vitro or in vivo the sequence of a siLNA orsiRNA compound need not be 100% complementary to its target nucleicacid. The terms “complementary” and “specifically hybridisable” thusimply that the siLNA or siRNA compound binds sufficiently strong andspecific to the target molecule to provide the desired interference withthe normal function of the target whilst leaving the function ofnon-target mRNAs unaffected

In the present context the term “conjugate” is intended to indicate aheterogenous molecule formed by the covalent attachment of a compound asdescribed herein to one or more non-nucleotide or non-polynucleotidemoieties. Examples of non-nucleotide or non-polynucleotide moietiesinclude macromolecular agents such as proteins, fatty acid chains, sugarresidues, glycoproteins, polymers, or combinations thereof. Typicallyproteins may be antibodies for a target protein. Typical polymers may bepolyethelene glycol.

In the present context, the term “C₁₋₆-alkyl” is intended to mean alinear or branched saturated hydrocarbon chain wherein the longestchains has from one to six carbon atoms, such as methyl, ethyl,n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl, tert-butyl, pentyl,isopentyl, neopentyl and hexyl. A branched hydrocarbon chain is intendedto mean a C₁₋₆-alkyl substituted at any carbon with a hydrocarbon chain.

In the present context, the term “C₁₋₄-alkyl” is intended to mean alinear or branched saturated hydrocarbon chain wherein the longestchains has from one to four carbon atoms, such as methyl, ethyl,n-propyl, isopropyl, n-butyl, isobutyl, sec-butyl and tert-butyl. Abranched hydrocarbon chain is intended to mean a C₁₋₄-alkyl substitutedat any carbon with a hydrocarbon chain.

When used herein the term “C₁₋₆-alkoxy” is intended to meanC₁₋₆-alkyl-oxy, such as methoxy, ethoxy, n-propoxy, isopropoxy,n-butoxy, isobutoxy, sec-butoxy, tert-butoxy, pentoxy, isopentoxy,neopentoxy and hexoxy.

In the present context, the term “C₂₋₆-alkenyl” is intended to mean alinear or branched hydrocarbon group having from two to six carbon atomsand containing one or more double bonds. Illustrative examples ofC₂₋₆-alkenyl groups include allyl, homo-allyl, vinyl, crotyl, butenyl,butadienyl, pentenyl, pentadienyl, hexenyl and hexadienyl. The positionof the unsaturation (the double bond) may be at any position along thecarbon chain.

In the present context the term “C₂₋₆-alkynyl” is intended to meanlinear or branched hydrocarbon groups containing from two to six carbonatoms and containing one or more triple bonds. Illustrative examples ofC₂₋₆-alkynyl groups include acetylene, propynyl, butynyl, pentynyl andhexynyl. The position of unsaturation (the triple bond) may be at anyposition along the carbon chain. More than one bond may be unsaturatedsuch that the “C₂₋₆-alkynyl” is a di-yne or enedi-yne as is known to theperson skilled in the art.

The term “carcinoma” is intended to indicate a malignant tumor ofepithelial origin. Epithelial tissue covers or lines the body surfacesinside and outside the body. Examples of epithelial tissue are the skinand the mucosa and serosa that line the body cavities and internalorgans, such as intestines, urinary bladder, uterus, etc. Epithelialtissue may also extend into deeper tissue layers to from glands, such asmucus-secreting glands.

The term “sarcoma” is intended to indicate a malignant tumor growingfrom connective tissue, such as cartilage, fat, muscles, tendons andbones.

The term “glioma”, when used herein, is intended to cover a malignanttumor originating from glial cells.

Compounds of the Invention

The present invention is, in part, based on the surprising finding thatLNA can be used to improve RNA interference by incorporating LNAmonomers in the sense and/or antisense strand of double-strandedpolynucleotides, such as siRNA. This is particularly surprising as thestructurally closely related ENA monomers strongly deteriorates RNAinterference, even for minimally modified siRNAs (Hamada et al.,Antisense and Nucl. Acid Drug Dev., 2002, 12, 301-309).

LNA exhibits unprecedented binding properties towards DNA and RNA targetsequences. In addition to these remarkable hybridization properties, LNAmonomers can be mixed and act cooperatively with DNA and RNA monomers aswell as with nucleotide analogues, such as 2′-O-alkyl-modified RNAmonomers. The unprecedented binding affinity of LNA towards DNA or RNAtarget sequences, and the ability to mix LNA monomers freely with DNAand RNA monomers and a range of nucleotide analogues has some importantconsequences for the development of effective and safe siRNA-likecompounds.

Natural dsDNA exists at physiological pH as a B-form helix, whereasdsRNA exists as an A-form helix. This morphological difference is due tothe difference in the preferred sugar conformations of the deoxyribosesand the riboses. At room temperature the furanose ring of deoxyriboseexists in an equilibrium between C2′-endo (S-type) and C3′-endo (N-type)conformation with an energy barrier of ˜2 kcal/mol (FIG. 1). TheC2′-endo (S-type) conformation gives rise to the B-form helix, whereasthe C3′-endo (N-type) conformation gives rise to the A-form helix. Fordeoxyribose the S-type conformation is slightly lowered in energycompared to the N-type and that explains why DNA is found in the S-typeconformation. For ribose the N-type conformation is preferred and,therefore, RNA adopts the A-form helix. It is known that the A-formhelix is associated with higher hybridisation stability.

LNA monomers are locking the conformation of the furanose ring in aconformation that corresponds to an extreme C3′-endo conformation. Thesemonomers are therefore mimicking the RNA conformation, and it has beenshown that the structure of the oligonucleotide and duplexes of themonomers are RNA-like (Petersen et al., J. Am. Chem. Soc., 2002, 124,5974-82). This means that the structure of RNA oligonucleotides andRNA/RNA duplexes in which LNA monomers are incorporated are notsignificantly changed compared to native RNA oligonucleotides andRNA/RNA duplexes. It was furthermore shown that the LNA monomers inducedRNA-like conformation when introduced in DNA. Thus, the LNA monomersimposed, in particular at the 3′ end, a strong degree of C3′-endoconformation (RNA like). If, for instance, every second or third residuein a DNA oligomer is replaced with LNA monomers, the overall structureof the oligonucleotide will become much like RNA. Thus, the duplexformed by such oligonucleotides will attain a structure resemblingnative A-form duplexes (RNA/RNA). It is part of this invention to usethis property of the LNA monomers to direct the conformation of DNAtowards RNA structure.

It will be appreciated that the unprecedented affinity of the LNA may beused to shorten the usual length of a siRNA oligonucleotide (from 21-35mers to, e.g., 12-20 mers) without compromising the affinity requiredfor pharmacological activity. As the intrinsic specificity of anoligonucleotide is inversely correlated to its length, such a shorteningwill significantly increase the specificity of the siLNA compoundtowards its RNA target. One aim of the invention is therefore, due tothe fact that the sequence of the humane genome is available and theannotation of its genes is rapidly progressing, to identify the shortestpossible, unique sequences in the target mRNA. Moreover, by reducing thesize of the oligonucleotides, and thereby ease the manufacturing processand lowering the manufacturing costs, it is believed that siLNAcompounds, such as those disclosed herein, have the potential to becomethe basis for RNAi therapy, and to become a commercially competitivetreatment which may be offered for a variety of diseases.

Accordingly, in its broadest aspect the present invention relates to adouble-stranded compound comprising a sense strand and an antisensestrand, wherein each strand comprises 12-35 nucleotides and wherein saidcompound comprises at least one locked nucleic acid (LNA) monomer. Thedouble-stranded compounds of the invention may be composed entirely ofLNA monomers or it may be composed of LNA monomers in any combinationwith DNA monomer, RNA monomers or nucleotide analogues.

As indicated above, the term “nucleotide” means a 2-deoxyribose (DNA)unit or a ribose (RNA) unit which is bonded through its number onecarbon to a nitrogenous base, such as adenine (A), cytosine (C), thymine(T), guanine (G) or uracil (U), and which is bonded through its numberfive carbon atom to an internucleoside linkage group (as defined above)or to a terminal group (as discussed below). Thus, the term “nucleotide”encompasses RNA units (or monomers) comprising a ribose unit which isbonded through its number one carbon to a nitrogenous base, such as A,C, T, G or U, and which is bonded through its number five carbon atom toa phosphate group or to a terminal group. As explained above, the term“nucleotide” also encompasses DNA units (or monomers) comprising a2-deoxyribose unit which is bonded through its number one carbon to anitrogenous base, such as A, C, T, G or U, and which is bonded throughits number five carbon atom to a phosphate group or to a terminal group.The term “nucleotide” also covers variants or analogues of such RNA andDNA monomers. For example, the 2′-OH (RNA) or 2′-H (DNA) group may besubstituted with —O—CH₃, —O—CH₂—CH₂—OCH₃, —O—CH₂—CH₂—CH₂—NH₂,—O—CH₂—CH₂—CH₂—OH or F. Other examples of a nucleotide analogues are LNAmonomers. Also, the internucleoside linkage group is not limited tophosphate (—O—P(O)₂—O—), but may include —O—P(O,S)—O—, —O—P(S)₂—O—,—S—P(O)₂—O—, —S—P(O,S)—O—, —S—P(S)₂—O—, —O—P(O)₂—S—, —O—P(O,S)—S—,—S—P(O)₂—S—, —O—PO(R^(H))—O—, O—PO(OCH₃)—O—, —O—PO(NR^(H))—O—,—O—PO(OCH₂CH₂S—R)—O—, —O—PO(BH₃)—O—, —O—PO(NHR^(H))—O—,—O—P(O)₂—NR^(H)—, —NR^(H)—P(O)₂—O—, —NR^(H)—CO—O—, —NR^(H)—CO—NR^(H)—,—O—CO—O—, —O—CO—NR^(H)—, —NR^(H)—CO—CH₂—, —O—CH₂—CO—NR^(H)—,—O—CH₂—CH₂—NR^(H)—, —CO—NR^(H)—CH₂—, —CH₂—NR^(H)—CO—, —O—CH₂—CH₂—S—,—S—CH₂—CH₂—O—, —S—CH₂—CH₂—S—, —CH₂—SO₂—CH₂—, —CH₂—CO—NR^(H)—,—O—CH₂—CH₂—NR^(H)—CO—, —CH₂—NCH₃—O—CH₂—, where R^(H) is hydrogen orC₁₋₄-alkyl. Furthermore, the nitrogenous base is not restricted to A, C,T, G or U, but may include other purines and pyrimidines, such as5-methylcytosine, isocytosine, pseudoisocytosine, 5-bromouracil,5-propynyluracil, 5-propyny-6-fluoroluracil, 5-methylthiazoleuracil,6-aminopurine, 2-aminopurine, inosine, 2,6-diaminopurine,7-propyne-7-deazaadenine, 7-propyne-7-deazaguanine and2-chloro-6-aminopurine. Other examples of nucleotide variants andanalogues which fall within the present definition of “nucleotide” aredescribed in Freier & Altmann (Nucl. Acid Res., 1997, 25, 4429-4443) andUhlmann (Curr. Opinion in Drug & Development (2000, 3(2): 293-213).Scheme 1 below illustrates selected examples of such nucleotide variantsand analogous. In conclusion, the compounds of the invention may containany of the above-mentioned nucleotides as long as the compound containsat least one LNA monomer in at least one of the strands.

As indicated above, the term “locked nucleic acid monomer” or “LNAmonomer” refers to a bicyclic nucleotide analogue and has the chemicalstructure shown in Scheme 2 below:

wherein

-   -   X is selected from the group consisting of O, S and NR^(H),        where R^(H) is H or alkyl, such as C₁₋₄-alkyl;    -   Y is (—CH₂)_(r), where r is an integer of 1-4; with the proviso        that when X═O then r is not 2.    -   Z and Z* are independently absent or selected from the group        consisting of an internucleoside linkage group, a terminal group        and a protection group; and    -   B is a nucleobase.

In a preferred embodiment of the invention, r is 1, i.e. a preferred LNAmonomer has the chemical structure shown in Scheme 3 below:

wherein Z, Z*, R^(H) and B are defined above.

In an even more preferred embodiment of the invention, X is O and r is1, i.e. an even more preferred LNA monomer has the chemical structureshown in Scheme 4 below:

wherein Z, Z* and B are defined above.

The structures shown in 3A and 3B above may also be referred to as the“beta-D form” and the “alpha-L form”, respectively. In a highlypreferred embodiment of the invention, the LNA monomer is the beta-Dform, i.e. the LNA monomer has the chemical structure indicated in 3Aabove.

As indicated above, Z and Z*, which serve for an internucleosidelinkage, are independently absent or selected from the group consistingof an internucleoside linkage group, a terminal group and a protectiongroup depending on the actual position of the LNA monomer within thecompound. It will be understood that in embodiments where the LNAmonomer is located at the 3′ end, Z is a terminal group and Z* is aninternucleoside linkage. In embodiments where the LNA monomer is locatedat the 5′ end, Z is absent and Z* is a terminal group. In embodimentswhere the LNA monomer is located within the nucleotide sequence, Z isabsent and Z* is an internucleoside linkage group.

Specific examples of internucleoside linkage groups include —O—P(O)₂—O—,—O—P(O,S)—O—, —O—P(S)₂—O—, —S—P(O)₂—O—, —S—P(O,S)—O—, —S—P(S)₂—O—,—O—P(O)₂—S—, —O—P(O,S)—S—, —S—P(O)₂—S—, —O—PO(R^(H))—O—, O—PO(OCH₃)—O—,—O—PO(NR^(H))—O—, —O—PO(OCH₂CH₂S—R)—O—, —O—PO(BH₃)—O—,—O—PO(NHR^(H))—O—, —O—P(O)₂—NR^(H)—, —NR^(H)—P(O)₂—O—, —NR″—CO—O—,—NR^(H)—CO—NR^(H)—, —O—CO—O—, —O—CO—NR^(H)—, —NR^(H)—CO—CH₂—,—O—CH₂—CO—NR^(H)—, —O—CH₂—CH₂—NR^(H)—, —CO—NR^(H)—CH₂—, —CH₂—NR^(H)—CO—,—O—CH₂—CH₂—S—, —S—CH₂—CH₂—O—, —S—CH₂—CH₂—S—, —CH₂—SO₂—CH₂—,—CH₂—CO—NR^(H)—, —O—CH₂—CH₂—NR^(H)—CO—, —CH₂—NCH₃—O—CH₂—, where R^(H) ishydrogen or C₁₋₄-alkyl.

In a preferred embodiment of the invention, the internucleoside linkagegroup is a phosphate group (—O—P(O)₂—O—), a phosphorothioate group(—O—P(O,S)—O—) or the compound may contain both phosphate groups andphosphorothioate groups.

Specific examples of terminal groups include terminal groups selectedfrom the group consisting of hydrogen, azido, halogen, cyano, nitro,hydroxy, Prot-O—, Act-O—, mercapto, Prot-S—, Act-S—, C₁₋₆-alkylthio,amino, Prot-N(R^(H))—, Act-N(R^(H))—, mono- or di(C₁₋₆-alkyl)amino,optionally substituted C₁₋₆-alkoxy, optionally substituted C₁₋₆-alkyl,optionally substituted C₂₋₆-alkenyl, optionally substitutedC₂₋₆-alkenyloxy, optionally substituted C₂₋₆-alkynyl, optionallysubstituted C₂₋₆-alkynyloxy, monophosphate including protectedmonophosphate, monothiophosphate including protected monothiophosphate,diphosphate including protected diphosphate, dithiophosphate includingprotected dithiophosphate, triphosphate including protectedtriphosphate, trithiophosphate including protected trithiophosphate,where Prot is a protection group for —OH, —SH and —NH(R^(H)), and Act isan activation group for —OH, —SH, and —NH(R^(H)), and R^(H) is hydrogenor C₁₋₆-alkyl.

Examples of phosphate protection groups include S-acetylthioethyl (SATE)and S-pivaloylthioethyl (t-butyl-SATE).

Still further examples of terminal groups include DNA intercalators,photochemically active groups, thermochemically active groups, chelatinggroups, reporter groups, ligands, carboxy, sulphono, hydroxymethyl,Prot-O—CH₂—, Act-O—CH₂—, aminomethyl, Prot-N(R^(H))—CH₂—,Act-N(R^(H))—CH₂—, carboxymethyl, sulphonomethyl, where Prot is aprotection group for —OH, —SH and —NH(R^(H)), and Act is an activationgroup for —OH, —SH, and —NH(R^(H)), and R^(H) is hydrogen or C₁₋₆-alkyl.

Examples of protection groups for —OH and —SH groups include substitutedtrityl, such as 4,4′-dimethoxytrityloxy (DMT), 4-monomethoxytrityloxy(MMT); trityloxy, optionally substituted 9-(9-phenyl)xanthenyloxy(pixyl), optionally substituted methoxytetrahydro-pyranyloxy (mthp);silyloxy, such as trimethylsilyloxy (TMS), triisopropylsilyloxy (TIPS),tert-butyldimethylsilyloxy (TBDMS), triethylsilyloxy,phenyldimethylsilyloxy; tert-butylethers; acetals (including two hydroxygroups); acyloxy, such as acetyl or halogen-substituted acetyls, e.g.chloroacetyloxy or fluoroacetyloxy, isobutyryloxy, pivaloyloxy,benzoyloxy and substituted benzoyls, methoxymethyloxy (MOM), benzylethers or substituted benzyl ethers such as 2,6-dichlorobenzyloxy(2,6-Cl₂Bzl). Moreover, when Z or Z* is hydroxyl they may be protectedby attachment to a solid support, optionally through a linker.

Examples of amine protection groups includefluorenylmethoxycarbonylamino (Fmoc), tert-butyloxycarbonylamino (BOC),trifluoroacetylamino, allyloxycarbonylamino (alloc, AOC),Z-benzyloxycarbonylamino (Cbz), substituted benzyloxycarbonylamino, suchas 2-chloro benzyloxycarbonylamino (2-CIZ), monomethoxytritylamino(MMT), dimethoxytritylamino (DMT), phthaloylamino, and9-(9-phenyl)xanthenylamino (pixyl).

The activation group preferably mediates couplings to other residuesand/or nucleotide monomers and after the coupling has been completed theactivation group is typically converted to an internucleoside linkage.Examples of such activation groups include optionally substitutedO-phosphoramidite, optionally substituted O-phosphortriester, optionallysubstituted O-phosphordiester, optionally substituted H-phosphonate, andoptionally substituted O-phosphonate. In the present context, the term“phosphoramidite” means a group of the formula —P(OR^(x))—N(R^(y))₂,wherein Rx designates an optionally substituted alkyl group, e.g.methyl, 2-cyanoethyl, or benzyl, and each of R^(y) designates optionallysubstituted alkyl groups, e.g. ethyl or isopropyl, or the group—N(R^(y))₂ forms a morpholino group (—N(CH₂CH₂)₂O). RX preferablydesignates 2-cyanoethyl and the two R^(y) are preferably identical anddesignates isopropyl. Accordingly, a particularly preferredphosphoramidite is N,N-diisopropyl-O-(2-cyanoethyl)phosphoramidite.

As indicated above, B is a nucleobase which may be of natural ornon-natural origin. Specific examples of nucleobases include adenine(A), cytosine (C), 5-methylcytosine (^(Me)C), isocytosine,pseudoisocytosine, guanine (G), thymine (T), uracil (U), 5-bromouracil,5-propynyluracil, 5-propyny-6-fluoroluracil, 5-methylthiazoleuracil,6-aminopurine, 2-aminopurine, inosine, 2,6-diaminopurine,7-propyne-7-deazaadenine, 7-propyne-7-deazaguanine and2-chloro-6-aminopurine. Preferred nucleobases include A, C, ^(Me)C, G, Tand U, in particular A, C, ^(Me)C, G and U.

In one embodiment of the invention, the sense strand comprises at leastone LNA monomer, such as 1-10 LNA monomers, e.g. 1-5 LNA monomers. Inanother embodiment of the invention, the antisense strand comprises atleast one LNA monomer, such as 1-10 LNA monomers, e.g. 1-5 LNA monomers.In a further embodiment of the invention, the sense strand comprises atleast one LNA monomer and the antisense strand comprises at least oneLNA monomer. For example, the sense strand typically comprises 1-10 LNAmonomers, such as 1-5 LNA monomers, and the antisense strand typicallycomprises 1-10 LNA monomers, such as 1-5 LNA monomers.

One particular advantage about the compounds of the invention is theirimproved stability in biological fluids, such as serum. Thus, oneembodiment of the invention includes the incorporation of LNA monomersinto a standard DNA or RNA oligonucleotide to increase the stability ofthe resulting siLNA compound in biological fluids e.g. through theincrease of resistance towards nucleases (endonucleases andexonucleases). Accordingly, the compounds of the invention will, due toincorporation of LNA monomers, exhibit an increased circulationhalf-life as a result of its increased melting temperature and/or itsincreased nuclease resistance. The extent of stability will depend onthe number of LNA monomers used, their position in the oligonucleotidesand the type of LNA monomer used. Compared to DNA and phosphorothioatesthe following order of ability to stabilise an oligonucleotide againstnucleolytic degradation can be established: DNA<<phosphorothioates,LNA-phosphordiester<LNA-phosphorothioates.

Therefore, compounds according to the invention which are particularlypreferred are such compounds which, when incubated in serum (e.g. human,bovine or mice serum), such as in 10% foetal bovine serum in aphysiological salt solution at 37° C. for 5 hours, are degraded to alesser extent than the corresponding dsRNA compound. Preferably, lessthan 25% of the initial amount of the compound of the invention isdegraded after 5 hours, more preferably less than 50% of the initialamount of the compound of the invention is degraded after 5 hours, evenmore preferably less than 75% of the initial amount of the compound ofthe invention is degraded after 5 hours. In another embodiment, it ispreferred that less than 25% of the initial amount of the compound ofthe invention is degraded after 10 hours, and even more preferred thatless than 50% of the initial amount of the compound of the invention isdegraded after 10 hours.

Given the fact that LNA synthesis is compatible with standard RNA/DNAsynthesis and that the LNA monomers mix freely with many contemporarynucleic acid analogues, nuclease resistance of siLNA compounds can befurther enhanced according to the invention by either incorporatingother analogues that display increased nuclease stability or byexploiting nuclease-resistant internucleoside linkages e.g.phosphoromonothioate, phosphorodithioate, and methylphosphonatelinkages, etc.

LNA monomers can be used freely in the design of siLNA at both 3′overhangs and the 5′ end of the sense strand with full activation of thesiLNA effect and down-regulation of protein production (>90% reduction).LNA monomers can be distributed quite freely over the sense strand inthe siLNA with maintaining high down-regulating capability (80%reduction). The 5′ end of the antisense strand in the siLNA can also bemodified by LNA monomers, thereby giving rise to down-regulatorycapabilities of up to 50-70%. Using a highly LNA monomer-substitutedantisense strand does not seem to give a down-regulatory effect,although it can not be ruled out that special design of that combinationcan elicit a RNAi effect. LNA monomer substitutions of the 3′ overhangsalong with the 5′ end of the sense strand of the siLNA give the highestreduction of protein levels. The 5′ end of the antisense strand is themost sensitive to the LNA monomer modification while many other sites ofmodification are better tolerated.

In one embodiment the siLNA compound is designed so that the LNAmonomers are incorporated in the compound in such a way that they arestrengthening the basepairs in the duplex at the 5′ end of the sensestrand. The helicase can there by be directed to unwinde from the other5′ end (antisense strand 5′ end). In this way the incorporation of theantisense/guiding strand into RISC can be controlled. The helicasestarts unwinding the siRNA duplex at the weakest binding end. Thereleased 3′ end is probably targeted for degradation while the remainingstrand is incorporated in the RISC. Efficient siRNAs show accumulationof the antisense/guiding strand and weaker base pairing in the 5′ end ofthe antisense/guiding strand. Unwanted side effects may possibly beavoided by having only the correct strand (the antisense/guiding strand)in RISC and not the unwanted sense strand (not complementary to thedesired target RNA).

The effect of incorporating LNA-monomers in the 5′ end of the antisensestrand can be seen from FIG. 11. The RNAi-impeding effect of a LNAresidue in the 5′-end can partially be removed by incorporating anopposite mismatch. In FIG. 11 this has been shown for both the Renillaand Firefly targets.

The RNAi-impeding effect of a LNA monomer incorporated at the 5′ end ofthe antisense strand can be almost eliminated by moving the LNA monomerone base position towards the 3′ end (FIG. 12). Moving the LNA-monomerfurther towards the 3′ end of the antisense strand does not affect thegene expression, but when the LNA monomer takes up position 10 or 12 asignificant decrease in the RNAi effect is observed. The RISC complexwill cleave the mRNA at a position opposite the position between 10 and11 of the antisense strand of the siRNA and, apparently, incorporationof the synthetic LNA monomer at that site impedes the cleavage by theRISC complex. When the LNA monomer is moved further along the antisensestrand this impeding effect is decreased.

As described above the helicase exhibits strand bias and will preferablyincorporate siRNA from the weakest binding end of the siRNA. Therefore,in principle, both strands in the siRNA duplex can be incorporated. Thisamong other properties of the RISC+siRNA system will give rise tooff-target effects. One way of reducing this is to incorporate the highaffinity LNA monomers. For the Ren1 site the 5′-nucleobase in theantisense strand is U that constitutes a “low” binding residue. The RISCcomplex will therefore read from this side and incorporate the antisensestrand (the correct strand). For the Rent and Ren3 sites the5′-nucleobase is C that constitutes “high” binding sites. For thesesites the 5′ end of the sense strand is positioned by an A and a Unucleobase that both constitutes “low” binding sites. The RISC cantherefore exhibit strand bias in this case and read partially from thesense strand (the wrong strand). By replacing the 5′-adenosine anduridine residues with the corresponding A- and U-LNA residues, thestrand bias is removed and the antisense strand is incorporated in theRISC complex (FIG. 13). Accordingly, LNA residues can decrease strandbias and increase the potency of the duplex. The siLNA according to thepresent invention preferably has an antisense sequence, which has least70%, more preferably 90-100% sequence identity to the target molecule.

As indicated above several particular designs augment the overallpotency applicability of native siRNA:

-   -   (a) “end capping” of the siRNA with LNA improves the nuclease        stability (FIGS. 2 and 15).    -   (b) Placing a LNA monomer towards the 5′-end of the sense strand        improves the potency of the siLNA compared to native siRNA        (“locking”). This is illustrated by the potency increase for        medium efficient targets (FIGS. 13 and 15).    -   (c) In the “LNA walk” (FIG. 12) it is shown that placing a LNA        monomer at the cleavage site of the RISC complex, e.g. at        position 10, calculated from the 5′ end in the antisense strand,        decreases the activity of the siRNA (“blocking”).

These basic observations are important for improving the overall potencyof siRNA. In optimised designs the 3′ ends should be “capped” with LNAmonomers thereby securing nuclease resistance (FIGS. 12 and 15). The 5′end of the sense strand should also be LNA modified to increase bindingto the antisense strand and thereby direct the helicase to incorporatefrom the “correct side” of the duplex. Such “locking” of the sense 5′end sense/antisense 3′ side of the duplex can be done by incorporatingat least one LNA monomer at either side of the duplex. Such modifiedduplexes may also contain LNA-LNA hydrogen bonding bases. Theobservation that gene silencing is reduced when LNA is incorporated inposition 10 or 12 in the antisense strand can be used in the reversedscenario. If the RISC complex should incorporate part of the sensestrand and thereby lead to unwanted off-target effects the potency ofthe unwanted incorporation could be reduced by incorporating LNA atposition 10 and 12 in the sense strand (“blocking”) as shown in FIG. 12.

Accordingly, in an interesting embodiment of the invention, the sensestrand comprises at least one LNA monomer located in at least one (suchas one) of the positions 9-13, counted from the 5′ end. Preferably, thesense strand comprises at least one LNA monomer located in at least one(such as one) of the positions 10-12, counted from the 5′ end. In aparticular interesting embodiment of the invention the sense strandcomprises a LNA monomer in position 10, position 12 or in both ofposition 10 and 12, counted from the 5′ end. Furthermore, it isparticularly preferred that the LNA monomer, if incorporated in position10, contains a nitrogenous base which is different from thenaturally-occurring RNA bases, i.e. different from A, C, G and U. In aparticular preferred embodiment the LNA monomer located at position 10(counted from the 5′ end) contains the nitrogenous base T.

It is known that LNA monomers incorporated into oligos will induce aRNA-like structure of the oligo and the hybrid that it may form. It hasalso been shown that LNA residues modify the structure of DNA residues,in particular when the LNA residues is incorporated in the proximity of3′ end. LNA monomer incorporation towards the 5′ end seems to have asmaller effect. This means that it is possible to modify RNA strandswhich contain DNA monomers, and if one or more LNA residues flank theDNA monomers they too will attain a RNA-like structure. Therefore, DNAand LNA monomer can replace RNA monomers and still the oligo will attainan overall RNA-like structure. As DNA monomers are considerably cheaperthan RNA monomers, easier to synthesise and more stable towardsnucleolytic degradation, such modifications will therefore improve theoverall use and applicability of siRNAs (see, e.g., FIG. 15).

Accordingly, it is preferred that at least one (such as one) LNA monomeris located at the 5′ end of the sense strand. More preferably, at leasttwo (such as two) LNA monomers are located at the 5′ end of the sensestrand.

In another preferred embodiment of the invention, the sense strandcomprises at least one (such as one) LNA monomer located at the ′3 endof the sense strand. More preferably, at least two (such as two) LNAmonomers are located at the 3′ end of the of the sense strand.

In a particular preferred embodiment of the invention, the sense strandcomprises at least one (such as one) LNA monomer located at the 5′ endof the sense strand and at least one (such as one) LNA monomer locatedat the 3′ end of the sense strand. Even more preferably, the sensestrand comprises at least two (such as two) LNA monomers located at the5′ end of the sense strand and at least two (such as two) LNA monomerslocated at the 3′ of the sense strand.

It is preferred that at least one (such as one) LNA monomer is locatedat the 3′ end of the antisense strand. More preferably, at least two(such as two) LNA monomers are located at the 3′ end of the antisensestrand. Even more preferably, at least three (such as three) LNAmonomers are located at the 3′ end of the antisense strand. In aparticular preferred embodiment of the invention, no LNA monomer islocated at or near (i.e. within 1, 2, or 3 nucleotides) the 5′ end ofthe antisense strand.

Thus, in a further embodiment of the invention, the LNA monomer may belocated in any position of the sense and antisense strands, except forthe ′5 end of the antisense strand.

In a highly preferred embodiment of the invention, the sense strandcomprises at least one LNA monomer at the 5′ end and at least one LNAmonomer at the 3′ end, and the antisense strand comprises at least oneLNA monomer at the 3′ end. More preferably, the sense strand comprisesat least one LNA monomer at the 5′ end and at least one LNA monomer atthe 3′ end, and the antisense strand comprises at least two LNA monomersat the 3′ end. Even more preferably, the sense strand comprises at leasttwo LNA monomers at the 5′ end and at least two LNA monomers at the 3′end, and the antisense strand comprises at least two LNA monomers at the3′ end. Still more preferably, the sense strand comprises at least twoLNA monomers at the 5′ end and at least two LNA monomers at the 3′ end,and the antisense strand comprises at least three LNA monomers at the 3′end. It will be understood that in the most preferred embodiment, noneof the above-mentioned compounds contain a LNA monomer which is locatedat the 5′ end of the antisense strand.

In a further interesting embodiment of the invention, the LNA monomer islocated close to the 3′ end, i.e. at position 2, 3 or 4, preferably atposition 2 or 3, in particular at position 2, calculated from the 3′end.

Accordingly, in a further very interesting embodiment of the invention,the sense strand comprises a LNA monomer located at position 2,calculated from the 3′ end. In another embodiment, the sense strandcomprises LNA monomers located at position 2 and 3, calculated from the3′ end.

In a particular preferred embodiment of the invention, the sense strandcomprises at least one (such as one) LNA monomer located at the 5′ endand a LNA monomer located at position 2 (calculated from the 3′ end). Ina further embodiment, the sense strand comprises at least two (such astwo) LNA monomers located at the 5′ end of the sense strand a LNAmonomer located at positions 2 (calculated from the 3′ end).

Furthermore, it is preferred that the antisense strand comprises a LNAmonomer at position 2, calculated from the 3′ end. More preferably, theantisense strand comprises LNA monomers in position 2 and 3, calculatedfrom the 3′ end. Even more preferably, the antisense strand comprisesLNA monomers located at position 2, 3 and 4, calculated from the 3′ end.In a particular preferred embodiment of the invention, no LNA monomer islocated at or near (i.e. within 1, 2, or 3 nucleotides) the 5′ end ofthe antisense strand.

In a highly preferred embodiment of the invention, the sense strandcomprises at least one LNA monomer at the 5′ end and a LNA monomer atposition 2 (calculated from the 3′ end), and the antisense strandcomprises a LNA monomer located at position 2 (calculated from the 3′end). More preferably, the sense strand comprises at least one LNAmonomer at the 5′ end and a LNA monomer at position 2 (calculated fromthe 3′ end), and the antisense strand comprises LNA monomers at position2 and 3 (calculated from the 3′ end). Even more preferably, the sensestrand comprises at least two LNA monomers at the 5′ end and LNAmonomers at position 2 and 3 (calculated from the 3′ end), and theantisense strand comprises LNA monomers at position 2 and 3 (calculatedfrom the 3′ end). Still more preferably, the sense strand comprises atleast two LNA monomers at the 5′ end and LNA monomers at position 2 and3 (calculated from the 3′ end), and the antisense strand comprises LNAmonomers at position 2, 3 and 4 (calculated from the 3′ end). It will beunderstood that in the most preferred embodiment, none of theabove-mentioned compounds contain a LNA monomer which is located at the5′ end of the antisense strand.

As indicated above, each strand comprises 12-35 nucleotides. It will beunderstood that these numbers refer to the total number of naturallyoccurring nucleotides, nucleotide variants and analogues, LNA monomers,etc., in the strand. Thus, the total number of such naturally occurringnucleotides, nucleotide variants and analogues, LNA monomers, etc., willnot be lower than 12 and will not exceed 35. In an interestingembodiment of the invention, each strand comprises 17-25 nucleotides,such as 20-22 or 20-21 nucleotides.

The compounds according to the invention may be blunt ended, and in oneparticular embodiment the siLNA compound of the invention is a 19-merand blunt ended. More preferably, however, at least one of the strandshas a 3′ overhang. Typically, the 3′ overhang will be of 1-7 nucleotides(or nucleotide variants or analogues or LNA monomers), preferably of 1-3nucleotides. Thus, it will be understood that the sense strand maycontain a 3′ overhang, the antisense strand may contain a 3′ overhang,or both of the sense and antisense strands may contain 3′ overhangs.

In a similar way, at least one of the strands may have a 5′ overhang.Typically, the 5′ overhang will be of 1-4 nucleotides (or nucleotidevariants or analogues or LNA monomers), preferably of 1-3 nucleotides.Thus, it will be understood that the sense strand may contain a 5′overhang, the antisense strand may contain a 5′ overhang, or both of thesense and antisense strands may contain 5′ overhangs. Evidently, thesense strand may contain both a 3′ and a 5′ overhang. Alternatively, theantisense strand may contain both a 3′ and a 5′ overhang.

Typically, the compounds of the invention will contain other residuesthan LNA monomers. Such other residues may be any of the residuesdiscussed in connection with the definition of “nucleotide” above, andinclude, for example, native RNA monomers, native DNA monomers as wellas nucleotide variants and analogues such as those mentioned inconnection with the definition of “nucleotide” above. Specific examplesof such nucleotide variants and analogues include, 2′-F, 2′-O-Me,2′-O-methoxyethyl (MOE), 2′-O-(3-aminopropyl) (AP), hexitol nucleic acid(HNA), 2′-F-arabino nucleic acid (2′-F-ANA) and D-cyclohexenylnucleoside (CeNA). Furthermore, the internucleoside linkage may be aphosphorodiester, phosphorothioate or N3′-P5′ phosphoroamidateinternucleoside linkages as described above.

In general, the individual strands of the compounds of the inventionwill contain at least about 5%, at least about 10%, at least about 15%or at least about 20% LNA monomer, based on total number of nucleotidesin the strand. In certain embodiments, the compounds of the inventionwill contain at least about 25%, at least about 30%, at least about 40%,at least about 50%, at least about 60%, at least about 70%, at leastabout 80% or at least about 90% LNA monomer, based on total number ofnucleotides in the strand.

As far as the LNA monomers are concerned, it will be understood that anyof the LNA monomers shown in Scheme 2 and 3 are useful for the purposesof the present invention. However, it is currently preferred that theLNA monomer is in the beta-D form, corresponding to the LNA monomersshown as compounds 3A, 3C and 3D. The currently most preferred LNAmonomer is the monomer shown as compound 3A in Scheme 3 and 4 above,i.e. the currently most preferred LNA monomer is the beta-D form ofoxy-LNA.

In a further embodiment of the invention, the compound of the inventionis linked to one or more ligands so as to form a conjugate. Theligand(s) serve(s) the role of increasing the cellular uptake of theconjugate relative to the non-conjugated compound. This conjugation cantake place at the terminal 5′-OH and/or 3′-OH positions, but theconjugation may also take place at the sugars and/or the nucleobases. Inparticular, the growth factor to which the antisense oligonucleotide maybe conjugated, may comprise transferrin or folate.Transferrin-polylysine-oligonucleotide complexes orfolate-polylysine-oligonucleotide complexes may be prepared for uptakeby cells expressing high levels of transferrin or folate receptor. Otherexamples of conjugates/lingands are cholesterol moieties, duplexintercalators such as acridine, poly-L-lysine, “end-capping” with one ormore nuclease-resistant linkage groups such as phosphoromonothioate, andthe like.

The preparation of transferrin complexes as carriers of oligonucleotideuptake into cells is described by Wagner et al, Proc. Natl. Acad. Sci.USA 87, 3410-3414 (1990). Cellular delivery of folate-macromoleculeconjugates via folate receptor endocytosis, including delivery of anantisense oligonucleotide, is described by Low et al, U.S. Pat. No.5,108,921 and by Leamon et al., Proc. Natl. Acad. Sci. 88, 5572 (1991).

The compounds or conjugates of the invention may also be conjugated orfurther conjugated to active drug substances, for example, aspirin,ibuprofen, a sulfa drug, an antidiabetic, an antibacterial agent, achemotherapeutic agent or an antibiotic.

The native RNA nucleobases are A, C, G and U. Using these in LNAmonomers will constitute a minimal modification. However, the bases^(Me)C (5′ methyl cytosine) and T (thymine) are readily used as LNAmonomers and can also be used in siLNA duplexes as shown herein (seeFIG. 16). It is anticipated that the nature of the bases used in theends of the siLNA will not significantly affect the functionality of thesiRNA molecule as along as they maintain their ability to hybridize tocomplementary bases if they occupy a base paired position in themolecule. However, when the LNA modifications are placed at internalpositions of the duplex, e.g. at position 10 (calculated from the 5′end), it must be anticipated that the nature of the nucleobase isimportant. Thus, the native bases, C and U, will perturbe the duplex toa smaller degree than the base modifications, T and ^(Me)C. Thisprovides subtle design possibilities. For instance if it is wanted to“block” the sense strand in the cleavage site e.g. at the 10th positionT or ^(Me)C should be used (if complementary), but if it is needed tomodify the antisense strand at the cleavage site e.g. position 10 U or Cshould be used (if complementary). One embodiment of the invention istherefore to include a modified nucleobase. An impediment of thenucleobase could be obtained by using bulkier groups than methyl, e.g.ethyl, propyl, phenyl or reporter groups like biotin. Thus, thedifferentiated recognition of the nucleobases by the RISC complex, orother enzymes provides an extra level of design opportunities of LNAmodified siRNA. Accordingly, in an interesting embodiment of theinvention, position 10 (calculated from the 5′ end) comprises T or^(Me)C.

In order to enable a rapid response to environmental and other changes,biological systems are typically constructed as dynamic systems, i.e. assystems in which the equilibrium state is maintained by the action ofboth activators and deactivators. Concerning the RISC complex it maytherefore be anticipated that the activated complex (i.e. the proteincomplex containing the intact oligonucleotide that catalyses thedestruction of the target) is subject to a deactivating activity, suchas for instance a nuclease activity that removes all or part of theoligonucleotide thereby disabling the function of the activated RISCcomplex. Alternatively, deactivation of the RISC complex may simply bedetermined by the off-rate of the oligonucleotide from the RISC complex,which, after dissociation, may not be able to re-associate.

Accordingly, in one interesting aspect the present invention relates tothe use of the compounds disclosed herein for enhancing the life-time ofthe active RISC complex thereby enhancing its duration-of-action. In oneembodiment of the invention this is achieved by increasing theresistance of the RNA component of the RISC complex to degradation bythe putative RNAse activity(ies) by incorporation of LNA and/or othernucleic acids analogues and/or by chemical modifications. In anotherembodiment of the invention the desired enhancement of the life-time ofthe active RISC complex is achieved by decreasing the off-rate of theRNA oligonucleotide from the RISC complex through introduction of LNAand/or other nucleic acid analogues and/or by chemical modificationsthat increases the affinity of the oligonucleotide for its bindingpartners in the RISC complex.

When designed as an inhibitor, the siLNAs of the invention bind to thetarget nucleic acid and modulate the expression of its cognate protein.Preferably, such modulation produces an inhibition of expression of atleast 10% or at least 20% compared to the normal expression level, morepreferably at least 30%, at least 40%, at least 50%, at least 60%, atleast 70%, at least 80%, or at least 90% inhibition compared to thenormal expression level.

Manufacture

The compounds of the invention may be produced using the polymerisationtechniques of nucleic acid chemistry, which is well known to a person ofordinary skill in the art of organic chemistry. Generally, standardoligomerisation cycles of the phosphoramidite approach (S. L. Beaucageand R. P. Iyer, Tetrahedron, 1993, 49, 6123; and S. L. Beaucage and R.P. Iyer, Tetrahedron, 1992, 48, 2223) may be used, but otherchemistries, such as the H-phosphonate chemistry or the phosphortriesterchemistry may also be used.

For some monomers longer coupling time and/or repeated couplings withfresh reagents and/or use of more concentrated coupling reagents may benecessary. However, in our hands, the phosphoramidites employed coupledwith a satisfactory >97% step-wise coupling yield. Thiolation of thephosphate may be performed by exchanging the normal oxidation, i.e. theiodine/pyridine/H₂O oxidation, with an oxidation process usingBeaucage's reagent (commercially available). As will be evident to theskilled person, other sulphurisation reagents may be employed.

Purification of the individual strands may be done using disposablereversed phase purification cartridges and/or reversed phase HPLC and/orprecipitation from ethanol or butanol. Gel electrophoresis, reversedphase HPLC, MALDI-MS, and ESI-MS may be used to verify the purity of thesynthesised LNA-containing oligonucleotides. Furthermore, solid supportmaterials having immobilised thereto a nucleobase-protected and 5′-OHprotected LNA are especially interesting for synthesis of theLNA-containing oligonucleotides where a LNA monomer is included at the3′ end. For this purpose, the solid support material is preferable CPGor polystyrene onto which a 3′-functionalised, optionally nucleobaseprotected and optionally 5′-OH protected LNA monomer is linked. The LNAmonomer may be attached to the solid support using the conditions statedby the supplier for that particular solid support material.

One aspect of the present invention is directed to a novel method forsynthesis of the compounds of the invention, which is characterised inthat the individual monomers, e.g. the LNA monomers and RNA monomers,are coupled using 1H-tetrazole or 5-ethylthio-1H-tetrazole. A furtherembodiment of this aspect is that the method involves a coupling timewhich is in the range of 200-1200 second, such as in the range of400-1200 seconds, preferably in the range of 600-900 seconds.

The targets to be modified according to the present invention may betargets involved in a number of basic biological mechanisms includingred blood cell proliferation, cellular proliferation, ion metabolism,glucose and energy metabolism, pH regulation and matrix metabolism. Theinvention described herein encompasses a method of preventing ortreating cancer comprising a therapeutically effective amount of atarget modulating siRNA compound to a human in need of such therapy.

Therapy and Pharmaceutical Compositions

As explained initially, the compounds of the invention will constitutesuitable drugs with improved properties. The design of a potent and safeRNAi drug requires the fine-tuning of diverse parameters such asaffinity/specificity, stability in biological fluids, cellular uptake,mode of action, pharmacokinetic properties and toxicity.

Accordingly, in a further aspect the present invention relates to apharmaceutical composition comprising a compound according to theinvention and a pharmaceutically acceptable diluent, carrier oradjuvant.

In a still further aspect the present invention relates to a compoundaccording to the invention for use as a medicament.

As will be understood dosing is dependent on severity and responsivenessof the disease state to be treated, and the course of treatment lastingfrom several days to several months, or until a cure is effected or adiminution of the disease state is achieved. Optimal dosing schedulescan be calculated from measurements of drug accumulation in the body ofthe patient. Optimum dosages may vary depending on the relative potencyof individual siLNAs. Generally it can be estimated based on EC50s foundto be effective in in vitro and in vivo animal models. In general,dosage is from 0.01 μg to 1 g per kg of body weight, and may be givenonce or more daily, weekly, monthly or yearly, or even once every 2 to10 years or by continuous infusion for hours up to several months. Therepetition rates for dosing can be estimated based on measured residencetimes and concentrations of the drug in bodily fluids or tissues.Following successful treatment, it may be desirable to have the patientundergo maintenance therapy to prevent the recurrence of the diseasestate.

Pharmaceutical Composition

It should be understood that the invention also relates to apharmaceutical composition, which comprises at least one compound of theinvention as an active ingredient. It should be understood that thepharmaceutical composition according to the invention optionallycomprises a pharmaceutical carrier, and that the pharmaceuticalcomposition optionally comprises further compounds, such aschemotherapeutic compounds, anti-inflammatory compounds, antiviralcompounds and/or immuno-modulating compounds.

The oligomeric compound comprised in this invention can be employed in avariety of pharmaceutically acceptable salts. As used herein, the termrefers to salts that retain the desired biological activity of theherein-identified compounds and exhibit minimal undesired toxicologicaleffects. Non-limiting examples of such salts can be formed with organicamino acid and base addition salts formed with metal cations such aszinc, calcium, bismuth, barium, magnesium, aluminum, copper, cobalt,nickel, cadmium, sodium, potassium, and the like, or with a cationformed from ammonia, N,N-dibenzylethylene-diamine, D-glucosamine,tetraethylammonium, or ethylenediamine.

In one embodiment of the invention the oligomeric compound may be in theform of a pro-drug. Oligonucleotides are by virtue negatively chargedions. Due to the lipophilic nature of cell membranes the cellular uptakeof oligonucleotides are reduced compared to neutral or lipophilicequivalents. This polarity “hindrance” can be avoided by using thepro-drug approach (see e.g. Crooke, R. M. (1998) in Crooke, S. T.Antisense research and Application. Springer-Verlag, Berlin, Germany,vol. 131, pp. 103-140). In this approach the oligonucleotides areprepared in a protected manner so that the oligo is neutral when it isadministered. These protection groups are designed in such a way thatthey can be removed when the oligo is taken up by the cells. Examples ofsuch protection groups are S-acetylthioethyl (SATE) orS-pivaloylthioethyl (t-butyl-SATE). These protection groups are nucleaseresistant and are selectively removed intracellulary.

Pharmaceutically acceptable binding agents and adjuvants may comprisepart of the formulated drug. Capsules, tablets and pills etc. maycontain for example the following compounds: microcrystalline cellulose,gum or gelatin as binders; starch or lactose as excipients; stearates aslubricants; various sweetening or flavouring agents. For capsules thedosage unit may contain a liquid carrier like fatty oils. Likewisecoatings of sugar or enteric agents may be part of the dosage unit. Theoligonucleotide formulations may also be emulsions of the activepharmaceutical ingredients and a lipid forming a micellular emulsion. Acompound of the invention may be mixed with any material that do notimpair the desired action, or with material that supplement the desiredaction. These could include other drugs including other nucleotidecompounds. For parenteral, subcutaneous, intradermal or topicaladministration the formulation may include a sterile diluent, buffers,regulators of tonicity and antibacterials. The active compound may beprepared with carriers that protect against degradation or immediateelimination from the body, including implants or microcapsules withcontrolled release properties. For intravenous administration thepreferred carriers are physiological saline or phosphate bufferedsaline. Preferably, an oligomeric compound is included in a unitformulation such as in a pharmaceutically acceptable carrier or diluentin an amount sufficient to deliver to a patient a therapeuticallyeffective amount without causing serious side effects in the treatedpatient.

The pharmaceutical compositions of the present invention may beadministered in a number of ways depending upon whether local orsystemic treatment is desired and upon the area to be treated.Administration may be (a) oral (b) pulmonary, e.g., by inhalation orinsufflation of powders or aerosols, including by nebulizer;intratracheal, intranasal, (c) topical including epidermal, transdermal,ophthalmic and to mucous membranes including vaginal and rectaldelivery; or (d) parenteral including intravenous, intraarterial,subcutaneous, intraperitoneal or intramuscular injection or infusion; orintracranial, e.g., intrathecal or intraventricular, administration. Inone embodiment the pharmaceutical composition is administered IV, IP,orally, topically or as a bolus injection or administered directly in tothe target organ. Pharmaceutical compositions and formulations fortopical administration may include transdermal patches, ointments,lotions, creams, gels, drops, sprays, suppositories, liquids andpowders. Conventional pharmaceutical carriers, aqueous, powder or oilybases, thickeners and the like may be necessary or desirable. Coatedcondoms, gloves and the like may also be useful. Preferred topicalformulations include those in which the compounds of the invention arein admixture with a topical delivery agent such as lipids, liposomes,fatty acids, fatty acid esters, steroids, chelating agents andsurfactants. Compositions and formulations for oral administrationinclude but is not restricted to powders or granules, microparticulates,nanoparticulates, suspensions or solutions in water or non-aqueousmedia, capsules, gel capsules, sachets, tablets or minitablets.Compositions and formulations for parenteral, intrathecal orintraventricular administration may include sterile aqueous solutionswhich may also contain buffers, diluents and other suitable additivessuch as, but not limited to, penetration enhancers, carrier compoundsand other pharmaceutically acceptable carriers or excipients.

Pharmaceutical compositions of the present invention include, but arenot limited to, solutions, emulsions, and liposome-containingformulations. These compositions may be generated from a variety ofcomponents that include, but are not limited to, preformed liquids,self-emulsifying solids and self-emulsifying semisolids. Delivery ofdrug to tumour tissue may be enhanced by carrier-mediated deliveryincluding, but not limited to, cationic liposomes, cyclodextrins,porphyrin derivatives, branched chain dendrimers, polyethylen-iminepolymers, nanoparticles and microspheres (Dass C R. J Pharm Pharmacol2002; 54(1):3-27). The pharmaceutical formulations of the presentinvention, which may conveniently be presented in unit dosage form, maybe prepared according to conventional techniques well known in thepharmaceutical industry. Such techniques include the step of bringinginto association the active ingredients with the pharmaceuticalcarrier(s) or excipient(s). In general the formulations are prepared byuniformly and intimately bringing into association the activeingredients with liquid carriers or finely divided solid carriers orboth, and then, if necessary, shaping the product. The compositions ofthe present invention may be formulated into any of many possible dosageforms such as, but not limited to, tablets, capsules, gel capsules,liquid syrups, soft gels and suppositories. The compositions of thepresent invention may also be formulated as suspensions in aqueous,non-aqueous or mixed media. Aqueous suspensions may further containsubstances which increase the viscosity of the suspension including, forexample, sodium carboxymethyl-cellulose, sorbitol and/or dextran. Thesuspension may also contain stabilizers. The compounds of the inventionmay also be conjugated to active drug substances, for example, aspirin,ibuprofen, a sulfa drug, an antidiabetic, an antibacterial or anantibiotic.

In another embodiment, compositions of the invention may contain one ormore siLNA compounds, targeted to a first nucleic acid and one or moreadditional siLNA compounds targeted to a second nucleic acid target. Twoor more combined compounds may be used together or sequentially.

The compounds disclosed herein are useful for a number of therapeuticapplications as indicated above. In general, therapeutic methods of theinvention include administration of a therapeutically effective amountof a siLNA to a mammal, particularly a human. In a certain embodiment,the present invention provides pharmaceutical compositions containing(a) one or more compounds of the invention, and (b) one or morechemotherapeutic agents. When used with the compounds of the invention,such chemotherapeutic agents may be used individually, sequentially, orin combination with one or more other such chemotherapeutic agents or incombination with radiotherapy. All chemotherapeutic agents known to aperson skilled in the art are here incorporated as combinationtreatments with compound according to the invention. Other activeagents, such as anti-inflammatory drugs, including but not limited tononsteroidal anti-inflammatory drugs and corticosteroids, antiviraldrugs, and immuno-modulating drugs may also be combined in compositionsof the invention. Two or more combined compounds may be used together orsequentially.

Cancer

In an even further aspect the present invention relates to the use of acompound according to the invention for the manufacture of a medicamentfor the treatment of cancer. In another aspect the present inventionconcerns a method for treatment of, or prophylaxis against, cancer, saidmethod comprising administering a compound of the invention or apharmaceutical composition of the invention to a patient in needthereof.

Such cancers may include lymphoreticular neoplasia, lymphoblasticleukemia, brain tumors, gastric tumors, plasmacytomas, multiple myeloma,leukemia, connective tissue tumors, lymphomas, and solid tumors.

In the use of a compound of the invention for the manufacture of amedicament for the treatment of cancer, said cancer may suitably be inthe form of a solid tumor. Analogously, in the method for treatingcancer disclosed herein said cancer may suitably be in the form of asolid tumor.

Furthermore, said cancer is also suitably a carcinoma. The carcinoma istypically selected from the group consisting of malignant melanoma,basal cell carcinoma, ovarian carcinoma, breast carcinoma, non-smallcell lung cancer, renal cell carcinoma, bladder carcinoma, recurrentsuperficial bladder cancer, stomach carcinoma, prostatic carcinoma,pancreatic carcinoma, lung carcinoma, cervical carcinoma, cervicaldysplasia, laryngeal papillomatosis, colon carcinoma, colorectalcarcinoma and carcinoid tumors. More typically, said carcinoma isselected from the group consisting of malignant melanoma, non-small celllung cancer, breast carcinoma, colon carcinoma and renal cell carcinoma.The malignant melanoma is typically selected from the group consistingof superficial spreading melanoma, nodular melanoma, lentigo malignamelanoma, acral melagnoma, amelanotic melanoma and desmoplasticmelanoma.

Alternatively, the cancer may suitably be a sarcoma. The sarcoma istypically in the form selected from the group consisting ofosteosarcoma, Ewing's sarcoma, chondrosarcoma, malignant fibroushistiocytoma, fibrosarcoma and Kaposi's sarcoma.

Alternatively, the cancer may suitably be a glioma.

A further embodiment is directed to the use of a compound according tothe invention for the manufacture of a medicament for the treatment ofcancer, wherein said medicament further comprises a chemotherapeuticagent selected from the group consisting of adrenocorticosteroids, suchas prednisone, dexamethasone or decadron; altretamine (hexalen,hexamethylmelamine (HMM)); amifostine (ethyol); aminoglutethimide(cytadren); amsacrine (M-AMSA); anastrozole (arimidex); androgens, suchas testosterone; asparaginase (elspar); bacillus calmette-gurin;bicalutamide (casodex); bleomycin (blenoxane); busulfan (myleran);carboplatin (paraplatin); carmustine (BCNU, BiCNU); chlorambucil(leukeran); chlorodeoxyadenosine (2-CDA, cladribine, leustatin);cisplatin (platinol); cytosine arabinoside (cytarabine); dacarbazine(DTIC); dactinomycin (actinomycin-D, cosmegen); daunorubicin(cerubidine); docetaxel (taxotere); doxorubicin (adriomycin);epirubicin; estramustine (emcyt); estrogens, such as diethylstilbestrol(DES); etopside (VP-16, VePesid, etopophos); fludarabine (fludara);flutamide (eulexin); 5-FUDR (floxuridine); 5-fluorouracil (5-FU);gemcitabine (gemzar); goserelin (zodalex); herceptin (trastuzumab);hydroxyurea (hydrea); idarubicin (idamycin); ifosfamide; IL-2(proleukin, aldesleukin); interferon alpha (intron A, roferon A);irinotecan (camptosar); leuprolide (lupron); levamisole (ergamisole);lomustine (CCNU); mechlorathamine (mustargen, nitrogen mustard);melphalan (alkeran); mercaptopurine (purinethol, 6-MP); methotrexate(mexate); mitomycin-C(mutamucin); mitoxantrone (novantrone); octreotide(sandostatin); pentostatin (2-deoxycoformycin, nipent); plicamycin(mithramycin, mithracin); prorocarbazine (matulane); streptozocin;tamoxifin (nolvadex); taxol (paclitaxel); teniposide (vumon, VM-26);thiotepa; topotecan (hycamtin); tretinoin (vesanoid, all-trans retinoicacid); vinblastine (valban); vincristine (oncovin) and vinorelbine(navelbine). Suitably, the further chemotherapeutic agent is selectedfrom taxanes such as Taxol, Paclitaxel or Docetaxel.

Similarly, the invention is further directed to the use of a compoundaccording to the invention for the manufacture of a medicament for thetreatment of cancer, wherein said treatment further comprises theadministration of a further chemotherapeutic agent selected from thegroup consisting of adrenocorticosteroids, such as prednisone,dexamethasone or decadron; altretamine (hexalen, hexamethylmelamine(HMM)); amifostine (ethyol); aminoglutethimide (cytadren); amsacrine(M-AMSA); anastrozole (arimidex); androgens, such as testosterone;asparaginase (elspar); bacillus calmette-gurin; bicalutamide (casodex);bleomycin (blenoxane); busulfan (myleran); carboplatin (paraplatin);carmustine (BCNU, BiCNU); chlorambucil (leukeran); chlorodeoxyadenosine(2-CDA, cladribine, leustatin); cisplatin (platinol); cytosinearabinoside (cytarabine); dacarbazine (DTIC); dactinomycin(actinomycin-D, cosmegen); daunorubicin (cerubidine); docetaxel(taxotere); doxorubicin (adriomycin); epirubicin; estramustine (emcyt);estrogens, such as diethylstilbestrol (DES); etopside (VP-16, VePesid,etopophos); fludarabine (fludara); flutamide (eulexin); 5-FUDR(floxuridine); 5-fluorouracil (5-FU); gemcitabine (gemzar); goserelin(zodalex); herceptin (trastuzumab); hydroxyurea (hydrea); idarubicin(idamycin); ifosfamide; IL-2 (proleukin, aldesleukin); interferon alpha(intron A, roferon A); irinotecan (camptosar); leuprolide (lupron);levamisole (ergamisole); lomustine (CCNU); mechlorathamine (mustargen,nitrogen mustard); melphalan (alkeran); mercaptopurine (purinethol,6-MP); methotrexate (mexate); mitomycin-C(mutamucin); mitoxantrone(novantrone); octreotide (sandostatin); pentostatin (2-deoxycoformycin,nipent); plicamycin (mithramycin, mithracin); prorocarbazine (matulane);streptozocin; tamoxifin (nolvadex); taxol (paclitaxel); teniposide(vumon, VM-26); thiotepa; topotecan (hycamtin); tretinoin (vesanoid,all-trans retinoic acid); vinblastine (valban); vincristine (oncovin)and vinorelbine (navelbine). Suitably, said treatment further comprisesthe administration of a further chemotherapeutic agent selected fromtaxanes, such as Taxol, Paclitaxel or Docetaxel.

Alternatively stated, the invention is furthermore directed to a methodfor treating cancer, said method comprising administering a compound ofthe invention or a pharmaceutical composition according to the inventionto a patient in need thereof and further comprising the administrationof a further chemotherapeutic agent. Said further administration may besuch that the further chemotherapeutic agent is conjugated to thecompound of the invention, is present in the pharmaceutical composition,or is administered in a separate formulation.

Infectious Diseases

In a particular interesting embodiment of the invention, siLNA compoundsaccording to the invention are used for targeting Severe AcuteRespiratory Syndrome (SARS), which first appeared in China in November2002. According to the WHO over 8,000 people have been infectedworld-wide, resulting in over 900 deaths. A previously unknowncoronavirus has been identified as the causative agent for the SARSepidemic (Drosten C et al. N Engl Med 2003, 348, 1967-76; and Fouchier RA et al. Nature 2003, 423, 240). Identification of the SARS-CoV wasfollowed by rapid sequencing of the viral genome of multiple isolates(Ruan et al. Lancet 2003, 361, 1779-85; Rota P A et al. Science 2003,300, 1394-9; and Marra M A et al. Science 2003, 300, 399-404). Thissequence information immediately made possible the development of SARSantivirals by nucleic acid-based knock-down techniques such as siRNA.The nucleotide sequence encoding the SARS-CoV RNA-dependent RNApolymerase (Pol) is highly conserved throughout the coronavirus family.The Pol gene product is translated from the genomic RNA as a part of apolyprotein, and uses the genomic RNA as a template to synthesizenegative-stranded RNA and subsequently sub-genomic mRNA. The Pol proteinis thus expressed early in the viral life cycle and is crucial to viralreplication (see FIG. 10).

Accordingly, in a further another aspect the present invention relatesthe use of a compound according to the invention for the manufacture ofa medicament for the treatment of Severe Acute Respiratory Syndrome(SARS), as well as to a method for treating Severe Acute RespiratorySyndrome (SARS), said method comprising administering a compoundaccording to the invention or a pharmaceutical composition according tothe invention to a patient in need thereof.

It is contemplated that the compounds of the invention may be broadlyapplicable to a broad range of infectious diseases, such as diphtheria,tetanus, pertussis, polio, hepatitis B, hemophilus influenza, measles,mumps, and rubella.

Accordingly, in yet another aspect the present invention relates the useof a compound according to the invention for the manufacture of amedicament for the treatment of an infectious disease, as well as to amethod for treating an infectious disease, said method comprisingadministering a compound according to the invention or a pharmaceuticalcomposition according to the invention to a patient in need thereof.

Inflammatory Diseases

The inflammatory response is an essential mechanism of defense of theorganism against the attack of infectious agents, and it is alsoimplicated in the pathogenesis of many acute and chronic diseases,including autoimmune disorders. In spite of being needed to fightpathogens, the effects of an inflammatory burst can be devastating. Itis therefore often necessary to restrict the symptomatology ofinflammation with the use of anti-inflammatory drugs. Inflammation is acomplex process normally triggered by tissue injury that includesactivation of a large array of enzymes, the increase in vascularpermeability and extravasation of blood fluids, cell migration andrelease of chemical mediators, all aimed to both destroy and repair theinjured tissue.

In yet another aspect, the present invention relates to the use of acompound according to the invention for the manufacture of a medicamentfor the treatment of an inflammatory disease, as well as to a method fortreating an inflammatory disease, said method comprising administering acompound according to the invention or a pharmaceutical compositionaccording to the invention to a patient in need thereof.

In one preferred embodiment of the invention, the inflammatory diseaseis a rheumatic disease and/or a connective tissue diseases, such asrheumatoid arthritis, systemic lupus erythematous (SLE) or Lupus,scleroderma, polymyositis, inflammatory bowel disease, dermatomyositis,ulcerative colitis, Crohn's disease, vasculitis, psoriatic arthritis,exfoliative psoriatic dermatitis, pemphigus vulgaris and Sjorgren'ssyndrome, in particular inflammatory bowel disease and Crohn's disease.

Alternatively, the inflammatory disease may be a non-rheumaticinflammation, like bursitis, synovitis, capsulitis, tendinitis and/orother inflammatory lesions of traumatic and/or sportive origin.

Other Uses

The siRNA compounds of the present invention can be utilized for asresearch reagents for diagnostics, therapeutics and prophylaxis. Inresearch, the siRNA may be used to specifically inhibit the synthesis oftarget genes in cells and experimental animals thereby facilitatingfunctional analysis of the target or an appraisal of its usefulness as atarget for therapeutic intervention. In diagnostics the siRNAoligonucleotides may be used to detect and quantitate target expressionin cell and tissues by Northern blotting, in-situ hybridisation orsimilar techniques. For therapeutics, an animal or a human, suspected ofhaving a disease or disorder, which can be treated by modulating theexpression of target is treated by administering the siRNA compounds inaccordance with this invention. Further provided are methods of treatingan animal particular mouse and rat and treating a human, suspected ofhaving or being prone to a disease or condition, associated withexpression of target by administering a therapeutically orprophylactically effective amount of one or more of the siRNA compoundsor compositions of the invention.

The invention is further illustrated in a non-limiting manner by thefollowing examples.

EXAMPLES Abbreviations

-   DMT: Dimethoxytrityl-   DCI: 4,5-Dicyanoimidazole-   DMAP: 4-Dimethylaminopyridine-   DCM: Dichloromethane-   DMF: Dimethylformamide-   THF: Tetrahydrofuran-   DIEA: N,N-diisopropylethylamine-   PyBOP: Benzotriazole-1-yl-oxy-tris-pyrrolidino-phosphonium    hexafluorophosphate-   Bz: Benzoyl-   Ibu: Isobutyryl-   Beaucage: 3H-1,2-Benzodithiole-3-one-1,1-dioxide-   GL3+: 5′-cuuacgcugaguacuucga_(d)t_(d)t-3′,-   GL3−: 5′-ucgaaguacucagcguaag_(d)t_(d)t-3′-   NPY+: 5′-ugagagaaagcacagaaaa_(d)t_(d)t-3′-   NPY−: 5′-uuuucugugcuuucucuca_(d)t_(d)t-3′-   RL+: 5′-aucugaagaaggagaaaaa_(d)t_(d)t-3′-   RL−: 5′-uuuuucuccuucuucagau_(d)t_(d)t-3′-   Small letters without prefix: RNA monomer-   Small letters with “d” prefix: DNA monomer

Example 1: Monomer Synthesis

The preparation of LNA monomers is described in great detail in thereferences Koshkin et al., J. Org. Chem., 2001, 66, 8504-8512, andPedersen et al., Synthesis, 2002, 6, 802-809 as well as in referencesgiven therein. Where the Z and Z* protection groups wereoxy-N,N-diisopropyl-O-(2-cyanoethyl)phosphoramidite anddimethoxytrityloxy such compounds were synthesised as described in WO03/095467; Pedersen et al., Synthesis 6, 802-808, 2002; Sorensen et al.,J. Am. Chem. Soc., 124, 2164-2176, 2002; Singh et al., J. Org. Chem. 63,6078-6079, 1998; and Rosenbohm et al., Org. Biomol. Chem. 1, 655-663,2003. All cytosine-containing monomers were replaced with5-methyl-cytosine monomers for all couplings. All LNA monomers used werebeta-D-oxy LNA (compound 3A).

Example 2: Oligonucleotide Synthesis

All syntheses were carried out in 1 μmole scale on a MOSS Expediteinstrument platform. The synthesis procedures were carried outessentially as described in the instrument manual.

Preparation of LNA Succinyl Hemiester

5′O-DMT-3″hydroxy-LNA monomer (500 mg), succinic anhydride (1.2 eq.) andDMAP (1.2 eq.) were dissolved in DCM (35 ml). The reaction mixture wasstirred at room temperature overnight. After extraction with NaH₂PO₄,0.1 M, pH 5.5 (2×), and brine (1×), the organic layer was further driedwith anhydrous Na₂SO₄, filtered, and evaporated. The hemiesterderivative was obtained in a 95% yield and was used without any furtherpurification.

Preparation of LNA-CPG (Controlled Pore Glass)

The above-prepared hemiester derivative (90 μmole) was dissolved in aminimum amount of DMF. DIEA and pyBOP (90 μmole) were added and mixedtogether for 1 min. This pre-activated mixture was combined withLCAA-CPG (500 Å, 80-120 mesh size, 300 mg) in a manual synthesiser andstirred. After 1.5 h stirring at room temperature, the support wasfiltered off and washed with DMF, DCM and MeOH. After drying the loadingwas determined to be 57 μmol/g (see Tom Brown, Dorcas J. S. Brown.Modern machine-aided methods of oligodeoxyribonucleotide synthesis. In:F. Eckstein, editor. Oligonucleotides and Analogues A PracticalApproach. Oxford: IRL Press, 1991: 13-14).

Phosphorothioate Cycles

5′-O-DMT (A(bz), C(bz), G(ibu) or T) linked to CPG were deprotectedusing a solution of 3% trichloroacetic acid (v/v) in dichloromethane.The CPG was washed with acetonitrile. Coupling of phosphoramidites(A(bz), G(ibu), 5-methyl-C(bz)) or T-β-cyanoethylphosphoramidite) wasperformed by using 0.08 M solution of the 5′O-DMT-protected amidite inacetonitrile and activation was done by using DCI (4,5-dicyanoimidazole)in acetonitrile (0.25 M). The coupling reaction was carried out for 2min. Thiolation was carried out by using Beaucage reagent (0.05 M inacetonitrile) and was allowed to react for 3 min. The support wasthoroughly washed with acetonitrile and the subsequent capping wascarried out by using standard solutions (CAP A) and (CAP B) to capunreacted 5′ hydroxyl groups. The capping step was then repeated and thecycle was concluded by acetonitrile washing.

LNA Unit Cycles

5′-O-DMT (A(bz), C(bz), G(ibu) or T) linked to CPG was deprotected byusing the same procedure as described above. Coupling was performed byusing 5′-O-DMT-A(bz), C(bz), G(ibu) or T-β-cyanoethylphosphoramidite(0.1 M in acetonitrile) and activation was done by DCI (0.25 M inacetonitrile). The coupling reaction was carried out for 7 minutes.Capping was done by using standard solutions (CAP A) and (CAP B) for 30sec. The phosphite triester was oxidized to the more stable phosphatetriester by using a standard solution of I₂ and pyridine in THF for 30sec. The support was washed with acetonitrile and the capping step wasrepeated. The cycle was concluded by thorough acetonitrile wash.

Cleavage and Deprotection

The oligonucleotides were cleaved from the support and the β-cyanoethylprotecting group removed by treating the support with 35% NH₄OH for 1 hat room temperature. The support was filtered off and the baseprotecting groups were removed by raising the temperature to 65° C. for4 hours. Ammonia was then removed by evaporation.

Purification

The oligos were either purified by reversed-phase-HPLC (RP-HPLC) or byanion exchange chromatography (AIE):

RP-HPLC:

Column: VYDAC™, Cat. No. 218TP1010 (vydac)

Flow rate: 3 ml/min

Buffer: A (0.1 M ammonium acetate, pH 7.6)

-   -   B (acetonitrile)        Gradient:

Time 0 10 18 22 23 28 B % 0 5 30 100 100 0AIE:Column: Resource™ 15Q (amersham pharmacia biotech)Flow rate: 1.2 ml/minBuffer: A (0.1 M NaOH)

-   -   B (0.1 M NaOH, 2.0 M NaCl)        Gradient:

Time 0 1 27 28 32 33 B % 0 25 55 100 100 0Tm Measurement

Melting curves were recorded on a Perkin Elmer UV/VIS spectrophotometerlambda 40 attached to a PTP-6 Peltier System. Oligonucleotides weredissolved in salt buffer (10 mM phosphate buffer, 100 mM NaCl, 0.1 mMEDTA, pH 7.0) at a concentration of 1.5 μM and using 1 cm path-lengthcells. Samples were denatured at 95° C. for 3 min and slowly cooled to20° C. prior to measurements. Melting curves were recorded at 260 nmusing a heating rate of 1° C./min, a slit of 2 nm and a response of 0.2sec. Tm values were obtained from the maximum of the first derivative ofthe melting curves.

Example 3: Synthesis of LNA/RNA Oligonucleotides

Synthesis

LNA/RNA oligonucleotides were synthesized DMT-off on a 1.0 μmole scaleusing an automated nucleic acid synthesiser (MOSS Expedite 8909) andusing standard reagents. 1H-tetrazole or 5-ethylthio-1H-tetrazole wereused as activators. The LNA A^(Bz), G^(iBu) and T phosphoramiditeconcentration was 0.1 M in anhydrous acetonitrile. The ^(Me)C^(Bz) wasdissolved in 15% THF in acetonitrile. The coupling time for all monomercouplings was 600 secs. The RNA phosphoramidites (Glen Research,Sterling, Va.) were N-acetyl and 2′-O-triisopropylsilyloxymethyl (TOM)protected. The monomer concentration was 0.1 M (anhydrous acetonitrile)and the coupling time was 900 secs. The oxidation time was set to be 50sec. The solid support was DMT-LNA-CPG (1000 Å, 30-40 μmole/g).

Work-Up and Purification

Cleavage from the resin and nucleobase/phosphate deprotection wascarried out in a sterile tube by treatment with 1.5 ml of a methylaminesolution (1:1, 33% methylamine in ethanol:40% methylamine in water) at35° C. for 6 h or left overnight. The tube was centrifuged and themethylamine solution was transferred to second sterile tube. Themethylamine solution was evaporated in a vacuum centrifuge. To removethe 2′-O-protection groups the residue was dissolved in 1.0 ml 1.0 MTBAF in THF and heated to 55° C. for 15 min. and left at 35° C.overnight. The THF was evaporated in a vacuum centrifuge leaving a lightyellow gum, which was neutralised with approx. 600 μl (total samplevolume: 1.0 ml) of RNase-free 1.0 M Tris-buffer (pH 7). The mixture washomogenised by shaking and heating to 65° C. for 3 min. Desalting of theoligonucleotides was performed on NAP-10 columns (Amersham Biosciences,see below). The filtrate from step 4 (see below) was collected andanalysed by MALDI-TOF and gel electroforesis (16% sequencing acrylamidegel (1 mm), 0.9% TBE [Tris: 89 mM, Boric acid: 89 mM, EDTA: 2 mM, pH8.3] buffer, ran for 2 h at 20 W as the limiting parameter. The gel wasstained in CyberGold (Molecular Probes, 1:10000 in 0.9×TBE) for 30 minfollowed by scanning in a Bio-Rad FX Imager). The concentration of theoligonucleotide was measured by UV-spectrometry at 260 nm.

Scheme A, Desalting on NAP-10 Columns:

Step Reagent Operation Volume Remarks 1 — Empty storage — Discard buffer2 H₂O (RNase- Wash 2 × full volume Discard free) 3 Oligo in buffer Load1.0 ml Discard (RNase-free) 4 H₂O (RNase- Elution 1.5 ml Collect - free)Contains oligo 5 H₂O (RNase- “Elution” 0.5 ml Collect - free) Containssalt + small amount of oligo

As will be appreciated by the skilled person, the most important issuesin the synthesis of the LNA/RNA oligos as compared to standardprocedures are that i) extended coupling times are necessary to achievegood coupling efficiency, and ii) the oxidation time has to be extendedto minimise the formation of deletion fragments. Furthermore, couplingof 2′-O-TOM protected phosphoramidites were superior to 2′-O-TBDMS.Taking this into account, the crude oligonucleotides were of suchquality that further purification could be avoided. MS analysis shouldbe carried out after the TOM-groups are removed.

Example 4: Improved Stability of siLNA as Compared to siRNA

The improved stability of siLNA as compared to siRNA is shown in FIG. 2.Both slightly- and more heavily-modified siRNA exhibited improvedstability. Stability was evaluated in 10% foetal bovine serum diluted ina physiological saline solution. The siRNA and siLNA were incubated inthe serum at 37° C. Samples were withdrawn at different time points andanalysed on 15% polyacrylamide TBE gels and stained with SYBR-gold(Molecular probes). Bands were quantified and plotted in a graph. Forthe unmodified siRNA compound an accumulation of an intermediate bandcan be seen (inbetween dsRNA and ssRNA) that has been identified to be adoublestranded 19-mer, i.e. siRNA with degraded 3′ overhangs. This wasnot observed for the corresponding siLNAs.

Example 5: Test of Design of siLNA in Mammalian Reporter System

The efficacy of different siLNA designs and combinations were firstassessed in a luciferase reported system in mammalian cell culture. Theoligonucleotides used are shown in Table 1. Sense and the correspondingantisense oligonucleotides were hybridised to generate double strands,i.e. siRNA or siLNA.

The cells used were the human embryonal kidney (HEK) 293 cell lines. HEK293 cells were maintained in DMEM supplemented with 10% foetal bovineserum, penicillin, streptomycine and glutamine (Invitrogen, Paisely,UK). The plasmids used were pGL3-Control coding for firefly luciferaceunder the control of the SV40 promoter and enhancer and pRL-TK codingfor Renilla luciferase under the control of HSV-TK promoter (Promega,Madison, Wis., USA).

Transfection

One day before transfection cells were seeded in 500 μl medium in24-well plates in order to adhere and reach a confluency of 70 to 90% atthe time of transfection. Cells were seeded in the medium withoutantibiotics and changed to 500 μl Opti-MEM I just before adding thetransfection mix to the cells. A standard co-transfection mix wasprepared for triplicate wells by separately adding 510 ng pGL3-Control,51 ng pRL-TK and 340 ng siRNA to 150 μl Opti-MEM I (Invitrogen) and 3 μlLipofectAMINE 2000 (Invitrogen) to another 150 μl Opti-MEM I. The twosolutions were mixed and incubated at room temperature for 20-30 minutesbefore adding to the cells. 100 μl of the transfection mix was added toeach of the three wells. The final volume of medium plus transfectionmix was 600 μl. The siLNA or siRNA concentration corresponded to about13 nM. Cells were incubated with the transfection mix for 4 hours andthe medium was then changed with fully supplemented DMEM.

Dual-Luciferase Reporter Assay (Promega)

Cells were harvested in passive lysis buffer and assayed according tothe protocol (Promega) using a NovoSTAR 96-well format luminometer withsubstrate dispenser (BMG Labtechnologies, Offenburg, Germany). 10 μlsample was applied in each well of a 96 well plate and 50 μl LuciferaceAssay Reagent II (substrate for firefly luciferase) was added to a wellby the luminometer and measured. Then, 50 μl Stop and Glow (stopsolution for firefly luciferase and substrate for Renilla luciferase)was added and measured. The average of the luciferase activitiesmeasured for 10 sec. was used to calculate ratios between firefly andRenilla luciferase or the opposite.

Example 6: In Vitro Model: Assessment Off Efficacy on an EndogenousTarget

The cells used were the rat adrenal pheochromocytoma, PC12 cell lines.PC12 were maintained in DMEM supplemented with 10% horse serum, 5%foetal bovine serum, penicillin, streptomycine and glutamine. The SiLNAor siRNA transfection protocol for endogenous genes (like NPY in PC12cells) follows the same procedure as described above but withoutluciferase plasmids and only adding siRNA targeting NPY (since the NPYgene is endogenously expressed in PC12 cells). Final siLNA or siRNAconcentrations ranged from 1 to 100 nM. Cells were usually harvested 24to 48 hours post transfection and mRNA was extracted. mRNA levels weremeasured with Real-Time PCR. The down-regulation of the NPY target inPC12 is shown in FIG. 3.

Example 7: In Vitro Model: Analysis of Inhibition of Target

Expression by Real-Time PCR

SiLNA or siRNA gene silencing of a target can be assayed in a variety ofways known in the art. For example, target mRNA levels can be quantifiedby, e.g., Northern blot analysis, competitive polymetargete chainreaction (PCR), or real-time PCR. Real-time quantitative PCR ispresently preferred. RNA analysis can be performed on total cellular RNAor mRNA. Methods of RNA isolation and RNA analysis, such as Northernblot analysis, is routine in the art and is taught in, for example,Current Protocols in Molecular Biology, John Wiley and Sons.

Cells were harvested and mRNA was extracted. Standard real-time PCRprotocols were used to amplify target genes from mRNA with gene specificprimers along with a primer pair towards a housekeeping gene as internalcontrol (such as Cyclophilin). Down-regulation was expressed as a ratioof amount target mRNA to amount control mRNA. Real-time quantitative(PCR) can be conveniently accomplished using the commercially availableiQ Multi-Color Real Time PCR Detection System, available from BioRAD.

Example 8: In Vitro Analysis: SiRNA Inhibition of Reporter TargetExpression by siLNA Oligonucleotides

LNA Monomers could be Used to Modify Both Ends of the Sense Strand insiRNA with a maintained effect as compared to siRNA (>90% inhibition ofFirefly Luciferase expression compared to untreated samples). Theantisense strand could also be modified in the 3′ end without loss ofefficiency while a modification in the 5′ end of the antisense strandreduced the effect to 25-50% inhibition. By exchanging alluracil-containing residues to LNA thymines in the sense strand reducedthe effect to 80% inhibition. A similar modification of the antisensestrand abolished the effect (FIG. 4). Phosphorylation of the 5′ end ofthe siLNA antisense strand did not improve the reduction (20-30%reduction, data not shown). Similar experiments targeting RenillaLuciferase showed that both ends of the sense strand could be modifiedwith LNA monomers while the antisense strand tolerates 3′ end LNAmonomer modification (95% inhibition in all cases), but showed lessinhibition with both a 3′ and a 5′ end LNA modification. Still up to 75%inhibition was observed (FIG. 5). Stability of LNA/RNA was measured onall RNA uracil to LNA thymidine oligo (2189) in 100% rat serum, wherethe stability was similar to naked DNA oligos. An unmodified RNA singlestrand (GL3−) and unmodified double strand (GL3+/−) were degradedalready at time point zero (FIG. 6).

Example 9: In Vitro Analysis: siRNA Inhibition of Endogenous Target bysiLNA

Inhibition of Cytotoxicity

Cells were transfected with 85 nM of the respective siRNA or siLNA (SARS1-4, see FIG. 7) or with control siRNA targeting the firefly luciferasegene (Luc) or the rat neuropeptide Y (NPY) gene. Mock-transfected cellswere treated with Lipofectamine 2000 only and used as positive control.Uninfected cells were included as negative control. Transfected cellswere infected with either 60,000, 6,000 or 600 TCID₅₀ of SARS-CoV. After50 hours of infection, the CPE and the cytotoxicity was measured. Therewas a marked difference in CPE between the cells treated with the mosteffective siRNA, SARS 1, as compared to mock-transfected cells (FIG. 8).The cytotoxicity was determined as percent LDH release from treatedcells as compared to mock-transfected control cells. The percentinhibition of cytotoxicity was calculated as 100-percent cytotoxicity inthe siRNA treated sample. The four Pol-specific siRNA and siLNA hadvarious effects on cytotoxicity (FIG. 9). The most effective siRNA andsiLNA were the ones targeting the SARS 1 site, which reducedcytotoxicity and with up to 65% at 600 TCID₅₀. The SARS 3 site wasmedium efficient using siRNA at all three viral doses. However SARS 3became an equally efficient site as SARS 1 by using siLNA, also at allthree viral doses. The sites SARS 2 and SARS 4 did no show any effect bysiRNA or siLNA at any viral dose. The data represent mean and standarddeviation determined by three independent experiments in quadruplicate.

Virus and Cells

Vero cells were used for all cellular experiments. Cells were cultivatedin phenol red-free Eagle's MEM containing 5% FCS and 1% PEST at 37° C.and 5% CO₂. The Frankfurt 1 isolate (GenBank accession number AY291315,kindly provided by Dr. H. W. Doerr) was grown to high titers on Verocells. Supernatants from two T225 cell culture flasks were pooled andfrozen at −80° C. in 1 ml vials and constituted the viral stock. Thestock virus was identified as SARS-CoV by diagnostic reversetranscriptase PCR using the BNIoutS2 and BNIoutAs¹¹ primers and theCor-p-F2 and Cor-p-R1 primers². The virus stock was used in ten-folddilutions or at a fixed dilution to infect Vero cells in 96 well cellculture plates. The virus stock was diluted 600,000 times (determined bythe Reed-Muench method) to reach TCID₅₀ in 96 well cell culture plates.

The siLNA oligonucleotides were produced as described above. Thesequence are shown in FIG. 7.

Tranfections

Lipofectamine2000 (Invitrogen) was used to transfect the cells withsiRNA and siLNA. Transfection efficiency was high and most cell weretransfected. The transfection medium was changed to phenol red-freeEagle's MEM after four hours, and cells were grown overnight to form aconfluent monolayer.

Cytopathogenicity and Cytotoxicity

The cytopathogenic effect (CPE) on infected cells was detected as cellrounding and detachment from the cell culture plate. The CPE was scoredin a light microscope. The cytotoxicity was measured using acytotoxicity detection kit (LDH) (Roche, Germany). Mock-transfectedcells treated with lipofectamine2000 only were set as 100% cytotoxicitycaused by the virus infection at each viral dilution. Uninfected cellswere used to determine the background cytotoxicity. The percentcytotoxicity was determined as [((Abs490 sample−background)/(Abs490mock-transfected controls−background))×100]. The inhibition ofcytotoxicity was calculated as [(1−(Abs490 sample−background)/(Abs490mock-transfected controls−background))×100].

Example 10: Reduction of Off-Site Effects

Inhibition of SARS sense/antisense target in 3′UTR of firefly luciferasewas performed at 1.6 nM siRNA/siLNA with the plasmids: pS3Xs (pGL3 withSARS sense target), pS3Xas (pGL3 with SARS antisense target), and pGL3(without SARS target).

The SARS 3 target sequence was cloned in sense (sequence correspondingto the SARS mRNA) and antisense direction (complementary sequence to theSARS mRNA) in firefly luciferase 3′ UTR, between the luciferase codingregion and poly A in pGL3. pGL3 was cut with Xba I (between luc. stopcodon and poly A) and a SARS S3 target sequence DNA oligo duplex withXba I overhangs.

(SARS 3 target (SARS genomic position 14593) DNA oligo duplex with Xba Ioverhangs) 5′-ctaqcaaactgtcaaacccggtaattttc-3′ (sense, same as mRNA)3′-qtttgacagtttgggccattaaaaqqatc-5′ (antisense, complementary to themRNA)

Ligation of the oligo duplex resulted in two plasmid produces witheither sense or antisense target (pS3Xs: target in sense direction,pS3Xas: target in antisense direction). The two different plasmids weretransfected into separate HEK293 cell cultures along with controlplasmid pRL-TK and siRNA targeting SARS3 or siLNA targeting SARS3 (finalconcentration 1.6 nM), according to protocol described in Example 5.Cells were incubated for 24 hours, cells were harvested and luciferaseactivity measured as described in Example 5.

siLNA can inactivate the unwanted sense strand while maintaining fulleffect of the antisense strand. siRNA shows effect of both strands. SARS3 target sequence was cloned in both sense and antisense direction whereafter siLNA and siRNA where assayed for inhibitory effects on two thedifferent plasmids.

siRNA shows down-regulation of both sense target (part from SARS mRNAsequence, ˜90% reduction of luciferase activity) as well as theantisense target (complementary sequence to the SARS mRNA) (˜50%reduction). Hence both the sense and antisense strand in the siRNA havea down regulatory effect. However, siLNA SARS 3 shows equally goodeffect down-regulating the sense target (˜90% reduction) while there isno activity on the antisense target (0% reduction). Hence the antisensestrand in the siLNA maintains full effect while the effect of theunwanted sense strand is abolished. This means that siLNA can minimizeoff-targets by the sense strand by inactivating it to the RNAinterference machinery (FIG. 17).

Example 11: In Vivo Efficacy of siLNA

The purpose of this study was to test the in vivo efficacy of two antieGFP siRNAs which have been modified by incorporation of LNA monomers.The used compounds were 3029/3031 and 3030/3031.

In brief, female nude mice (NMRI nu/nu, Charles River Netherlands,Maastricht, The Netherlands) were injected with 15PC3 and Miapacaxenografts. The 15PC3 cells and Miapaca cells express eGFP as describedby Fluiter et al. (2002) Cancer Research 62, 2024-2028.

After two weeks of tumor growth the mice were subcutaneously fitted withOsmotic minipumps (Alzet 1007D, lot no. 10052-02 (7 day pumps) (DurectCorporation, Cupertino, Calif.)). These pumps were filled with either3029/3031 or 3030/3031 to give a dosage of 0.5 mg/kg/day. The mic weretreated for 5 days. At the 5th day the mice were sacrificed and thetumor fluorescence was imaged and measured using a LAS3000 luminesentimage analyser (Fujifilm). The fluorescence was quantified using AIDAsoftware (Raytest GmbH, Straubenhardt, Germany). After imaging thetumors were taken out and stored for protein analysis (western blot).The obtained results for 15PC3 are shown in FIG. 18. As can be seen thesiLNA compounds had a significant effect on tumor growth. Similarresults were obtained with the Miapaca xenograft model.

The siLNA was checked prior to implantation and after the experiment(leftover in the pump) using MALDI-tof analysis. The siLNA was purifiedby ion exchange on the purification plates from the Nucleave genotypingkit (Waters, Milford, Mass., USA) and analyzed using Matrix-assistedlaser desorption ionization time-of-flight mass spectrometry (MALDI-TOF)on a Biflex III MALDI (Brucker instruments, Leipzig, Germany). Data areshown in FIG. 20.

TABLE 1 Conc. No Sequence (5′→3′) (μM) Purity 2184 cuuacgcugaguacuucgaTT440 ~80% 2185 ^(Me)CuuacgcugaguacuucgaTT 320 ~70% 2186ucgaaguacucagcguaagTT 380 ~65% 2187 TcgaaguacucagcguaagTT 340 ~60% 2187-Phos-TcgaaguacucagcguaagTT 350 ~80% phos 2188 ^(Me)CTTcgcTagTacTTcgaTT410 ~50% 2189 TcgaagTacTcagcgTaagTT 390 ~55% 2189-Phos-TcgaagTacTcagcgTaagTT 330 ~80% phos 2699-1 uuuuucuccuucuucagauTT400 ~80% 2700-1 aucugaagaaggagaaaaaTT 400 ~80% 2701-1TuuuucuccuucuucagauTT 360 ~80% 2702-1 AucugaagaaggagaaaaaTT 430 ~80%2703-1 ^(Me)CTTacgcTgagTacTTcgaTT 500 ~80% Capital letters: Beta-D-oxyLNA monomer Small letters: RNA monomer Phos: 5′-phosphate ^(Me)C:5-methylcytosine

TABLE 2 No Sequence (5′→3′) 2780^(Me)CTTA^(Me)CG^(Me)CTGAGTA^(Me)CTT^(Me)CGATT 2781_(d)cT_(d)tA_(d)cG_(d)cT_(d)gA_(d)gT_(d)a^(Me)C_(d)tT_(d)cG_(d)aTT 2782_(d)cT_(d)t_(d)a^(Me)C_(d)g_(d)cT_(d)g_(d)aG_(d)t_(d)a^(Me)C_(d)t_(d)t^(Me)C_(d)g_(d)aTT2783 ^(Me)CuuAcGcuGaGua^(Me)Cuu^(Me)CgaTT 2784^(Me)C_(d)u_(d)u_(d)A_(d)cG_(d)c_(d)uG_(d)aG_(d)u_(d)a^(Me)C_(d)u_(d)u^(Me)C_(d)g_(d)aTT2785 u^(Me)CGAAGTA^(Me)CT^(Me)CAG^(Me)CGTAAGTT 2786u^(Me)C_(d)gA_(d)aG_(d)tA_(d)cT_(d)cA_(d)g^(Me)C_(d)gT_(d)aA_(d)gTT 2787u^(Me)C_(d)g_(d)aA_(d)g_(d)tA_(d)c_(d)t^(Me)C_(d)a_(d)g^(Me)C_(d)g_(d)tA_(d)a_(d)gTT2788 ucGaaGua^(Me)CucAgcGuAagTT 2789 u^(Me)CgaaguacucagcguaagTT 2790ucGaaguacucagcguaagTT 2792 ucgaAguacucagcguaagTT 2793ucgaaGuacucagcguaagTT 2794 ucgaaguAcucagcguaagTT 2795TgAgAgaaAgcAcAgaAaaTT 2796 TgagagaaagcacagaaaaTT 2797TuuucugugcuuucucucaTT Capital letters: Beta-D-oxy LNA monomer Smallletters without prefix: RNA monomer Small letters with “d” prefix: DNAmonomer ^(Me)C: 5-methylcytosine

TABLE 3 No Sequence (5′→3′) 2842-1 GgaugaggaaggcaauuuaTT 2843-1uaaauugccuuccucauccTT 2872-1 CugguacgauuucggugauTT 2845-1aucaccgaaaucguaccagTT 2846-1 AcugucaaacccgguaauuTT 2847-1aauuaccggguuugacaguTT 2848-1 GacaacuccuauucguaguTT 2849-1acuacgaauaggaguugucTT 2862-1 UccagaacaaaccaaacggTT 2863-1AaacaugcagaaaaugcugTT 2864-1 ucgaagua^(Me)CucagcguaagTT 2865-1ucgaaguacTcagcguaagTT 2866-1 ucgaaguacu^(Me)CagcguaagTT 2867-1ucgaaguacucAgcguaagTT 2865-U ucgaaguacAcagcguaagTT 3029GcugacccugaaguucaucTT 3030 G^(Me)CTgac^(Me)CcuGaagTTcaucTT 3031gaugaacuucagggucagcTT Capital letters: Beta-D-oxy LNA monomer Smallletters without prefix: RNA monomer ^(Me)C: 5-methylcytosine

The invention claimed is:
 1. A double-stranded compound comprising asense strand and an antisense strand, wherein each strand comprises17-25 nucleotides, wherein at least one of the strands has a 3′ overhangand wherein said compound comprises at least one locked nucleic acid(LNA) monomer located at the 5′ end of the sense strand, and wherein noLNA monomer is located at the 5′ end of the antisense strand.
 2. Thecompound according to claim 1, wherein the sense strand comprises 1-10LNA monomers.
 3. The compound according to claim 1, wherein at two LNAmonomers are located at the 5′ end of the sense strand.
 4. The compoundaccording to claim 1, wherein at least two LNA monomers are located atthe 5′ end of the sense strand.
 5. The compound according to claim 1,wherein at least one LNA monomer is located at the 3′ end of the sensestrand.
 6. The compound according to claim 1, wherein at least two LNAmonomers are located at the 3′ end of the sense strand.
 7. The compoundaccording to claim 1, wherein the antisense strand comprises 1-10 LNAmonomers.
 8. The compound according to claim 1, wherein at least one LNAmonomer is located at the 3′ end of the antisense strand.
 9. Thecompound according to claim 1, wherein at least two LNA monomers arelocated at the 3′ end of the antisense strand.
 10. The compoundaccording to claim 1, wherein at least three LNA monomers are located atthe 3′ end of the antisense strand.
 11. The compound according to claim1, wherein the sense strand comprises at least one LNA and the antisensestrand comprises at least one LNA monomer.
 12. The compound according toclaim 1, wherein the sense strand comprises 1-10 LNA monomers and theantisense strand comprises 1-10 LNA monomers.
 13. The compound accordingto claim 1, wherein the sense strand comprises at least one LNA monomerat the 5′ end and at least one LNA monomer at the 3′ end, and whereinthe antisense strand comprises at least one LNA monomer at the 3′ end.14. The compound according to claim 1, wherein the sense strandcomprises at least one LNA monomer at the 5′ end and at least one LNAmonomer at the 3′ end, and wherein the antisense strand comprises atleast two LNA monomers at the 3′ end.
 15. The compound according toclaim 1, wherein the sense strand comprises at least two LNA monomers atthe 5′ end and at least two LNA monomers at the 3′ end, and wherein theantisense strand comprises at least two LNA monomers at the 3′ end. 16.The compound according to claim 1, wherein the sense strand comprises atleast two LNA monomers at the 5′ end and at least two LNA monomers atthe 3′ end, and wherein the antisense strand comprises at least threeLNA monomers at the 3′ end.
 17. The compound according to claim 1,wherein the sense strand comprises at least one LNA monomer in at leastone of the positions 9-13 counted from the 5′ end.
 18. The compoundaccording to claim 1, wherein the sense strand comprises a LNA monomerin position
 10. 19. The compound according to claim 1, wherein the sensestrand comprises a LNA monomer in position
 11. 20. The compoundaccording to claim 1, wherein the sense strand comprises a LNA monomerin position
 12. 21. The compound according to claim 17, wherein thesense strand comprises at least one LNA monomer at the 5′ end and atleast one LNA monomer at the 3′ end, and wherein the antisense strandcomprises at least one LNA monomer at the 3′ end.
 22. The compoundaccording to claim 17, wherein the sense strand comprises at least oneLNA monomer at the 5′ end and at least one LNA monomer at the 3′ end,and wherein the antisense strand comprises at least two LNA monomers atthe 3′ end.
 23. The compound according to claim 17, wherein the sensestrand comprises at least two LNA monomers at the 5′ end and at leasttwo LNA monomers at the 3′ end, and wherein the antisense strandcomprises at least two LNA monomers at the 3′ end.
 24. The compoundaccording to claim 17, wherein the sense strand comprises at least twoLNA monomers at the 5′ end and at least two LNA monomers at the 3′ end,and wherein the antisense strand comprises at least three LNA monomersat the 3′ end.
 25. The compound according to claim 1, wherein eachstrand comprises 20-22 nucleotides.
 26. The compound according to claim17, wherein each strand comprises 20-22 nucleotides.
 27. The compoundaccording to claim 24, wherein each strand comprises 20-22 nucleotides.